Polyolefin compositions exhibiting heat resistivity, low hexane-extractives and controlled modulus

ABSTRACT

The subject invention provides a polymer mixture having high heat resistivity, low hexane extractive and controllably lower or higher modulus. The mixture is comprised of at least one first substantially linear ethylene polymer, Component (A), and at least one second ethylene polymer which is a homogeneously branched polymer, heterogeneously branched linear polymer or a non-short chain branched linear polymer. When fabricated into film, the mixture is characterized by a heat seal initiation temperature which is substantially lower than its Vicat softening point as well as a high ultimate hot tack strength. When fabricated as a molded article, the mixture is characterized by high microwave warp distortion while maintaining a lower modulus. The polymer mixture is particularly well-suited for use in multilayer film structures as a sealant layer for such applications as cook-in packages, hot-fill packages, and barrier shrink films. In molding applications, the mixture is well-suited as freezer-to-microwave food storage containers and lids which maintain good flexibility at low temperature to allow easy openability of such containers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/327,156, filed Oct.21, 1994, abandoned, which is related to the following pendingapplications: U.S. patent application Ser. No. 08/054,379, filed on Apr.28, 1993; U.S. patent application Ser. No. 08/010,958, filed on Jan. 29,1993; U.S. patent application Ser. No. 08/239,495, filed on May 9, 1994;and U.S. patent application Ser. No. 08/239,496, filed on May 9, 1994,the disclosures of all of which are incorporated herein by reference.

FIELD OF THE INVENTION

This invention pertains to a polyolefin composition comprising at leasttwo polymer material components. Particular embodiments of thisinvention, such a composition, or a film, coating or molding fabricatedfrom such a composition, will be characterized as having a high heatresistivity, high percent residual crystallinity, low level of hexaneextractives, low heat seal and hot tack initiation temperatures, highhot tack strength and controlled modulus.

BACKGROUND OF THE INVENTION

Although polyolefin resins have long found utility in food packaging andfood storage container applications, a polyolefin resin with the desiredbalance of properties in the form of a film, coating and molding has notbeen available to fabricators and packagers. An optimum polyolefin resinfor packaging and storage applications would possess a number of keyperformance properties. In particular, an optimum resin would becharacterized by a high percent residual crystallinity and/or high Vicatsoftening point (indicating high heat resistivity which is important,for example, for microwavable food container and in hot-fill filmpackaging applications); a controllably high or low modulus (indicatinggood dimensional stability which is important for efficient productloading and bag-making operations or indicating good openability ofrefrigerated food containers, respectively); a low heat seal and hottack temperature (indicating the ability to readily convert films andcoatings into packages); high tear, dart impact resistance and punctureresistance (indicating greater package or container integrity underabuse); and a low level of hexane extractives (indicating a lowertendency for low molecular weight impurities or polymer fractions tomigrate into sensitive packaged goods such as foodstuffs in food contactapplications).

Traditionally, enhancement of one particular resin property has requiredsome sacrifice with respect to another important resin property. Forinstance, low modulus, low heat seal and hot tack initiationtemperatures, high tear strength, high dart impact resistance and highpuncture resistance are typically achieved by increasing the comonomercontent of the resin. In contrast, high crystallinity, high Vicatsoftening points, high modulus and low levels of n-hexane extractivesare typically achieved by decreasing the comonomer content of the resin.Accordingly, improving the resin with respect to one class of propertieshas been historically achieved to the detriment of other properties.

One particular problem which has confronted industry is that the Vicatsoftening point of a resin and the heat seal initiation or hot tackinitiation temperatures of a film layer fabricated from such a resinhave been historically viewed as directly related. That is, whilepreferred resins will have a high Vicat softening point to promote heatresistivity, such improved heat resistivity traditionally comes at thecost of increased heat seal initiation and hot tack temperatures, whichimposes decreased packaging line speeds and increased energy costs uponthe package fabricator. Also, conventional resins typically have heatseal and hot tack initiation temperatures that either approximate theirrespective Vicat softening points or, more undesirably, are higher thantheir respective Vicat softening points. Thus, it is presently desirableto maximize the difference between the Vicat softening point of a resinand the heat seal and/or hot tack initiation temperature of a film layerfabricated from that resin as well as to provide polymer compositionsthat are characterized as having initiation temperatures more than 6° C.lower than their respective Vicat softening points such that packageshaving high heat resistivity and high ultimate hot strength may be moreeconomically prepared.

Another particular problem which has confronted industry is that whileethylene alpha-olefin polymers having a higher comonomer content, (i.e.,a density less than about 0.900 g/cc) yield films and coatings thatexhibit good performance in terms of low heat seal and hot tackinitiation temperatures, tear strength, dart impact resistance andpuncture resistance, such polymers either exhibit excessive n-hexaneextractives or are substantially soluble in n-hexane. In contrast tosimple extraction, which pertains to the solubilizing of low molecularweight impurities, polymer fractions or degradation products whichrepresent only small portions of the total polymer, substantiallycomplete solubility in n-hexane is attributable to higher degrees ofpolymer amorphosity, i.e., a lower degree of crystallinitycharacteristic of interpolymers having a higher comonomer content.

Hexane-soluble materials and materials with high n-hexane extractiveslevels generally are not acceptable for use in direct food contactapplications, such as sealant layers in multilayer film packages orinjection molded food storage containers. Even where these materials areused for food packaging and storage in general, or for packaging andstoring taste and odor sensitive goods, a substantial barrier material(such as, for example, aluminum foil) must be used between the materialand the packaged or stored item. Accordingly, industry has historicallybeen limited with respect to the utilization of lower density ethylenealpha-olefin resins having excellent heat seal and hot tack initiationperformance and abuse properties in food contact applications as well asother applications involving taste or odor sensitive goods. Thus, it isalso desirable to provide an ethylene alpha-olefin polymer compositionhaving the beneficial performance attributes of ethylene alpha-olefinresins having densities less than 0.900 g/cc (e.g., attributes whichindicate their utility as films and coatings having improved abuseproperties and lower heat seal and hot tack initiation temperatures),but which are characterized by reduced levels of hexane extractives,making such polymer compositions suitable for use in food contactapplications.

Still another problem that has plagued the plastic industry is theunavailability of optimum molding compositions for fabricating improvedlids for freezer-to-microwave food containers. Such compositions shouldhave good flexibility (i.e., a lower flexural modulus) to insure easyopenability while the container is still at freezer or refrigeratortemperatures, yet such compositions should also have good heatresistance to prevent undo melting, softening or distortion of lids whenthe container and foodstuff is microwaved. Easy lid openability andremoval is particularly important for consumers with weak or weakenedhand muscles and coordination. Thus, it also desirable to provideethylene alpha-olefin molding compositions with improved heat resistancewhile maintaining a lower flexural modulus.

U.S. Pat. No. 4,429,079 to Shibata, et al., discloses anethylene/alpha-olefin copolymer blend composition comprising a mixtureof (A) 95-40 weight percent of a random copolymer of ethylene and analpha-olefin having 5 to 10 carbon atoms which has a melt index of 0.1to 20 g/10 min., a density of 0.910 to 0.940 g/cc, a crystallinity byX-rays of 40 to 70%, a melting point of 115° to 130° C., and an ethylenecontent of 94 to 99.5 mol %; and (B) 5 to 60% by weight of a randomcopolymer of ethylene and an alpha-olefin having 3 to 10 carbon atomswhich has a melt index of 0.1 to 50 g/10 min., a density of 0.870 to0.900 g/cc, a crystallinity by X-rays of 5 to 40%, a melting point of40° to 100° C. and an ethylene content of 85 to 95 mol %. The (A)component polymer is said to be produced by a titanium catalyst systemand the (B) component polymer is said to be produced by a vanadiumcatalyst. Both of these catalyst systems are known as Ziegler typecatalysts which produce linear ethylene alpha-olefin polymers. That is,the polymer will have a linear molecular backbone without any long chainbranching. Further, the (A) component polymer will also have aheterogeneously branched short chain distribution, while the (B)component polymer will have a homogeneously branched short chaindistribution. The film fabricated from the Shibata et al. compositionallegedly has good low-temperature heat sealability, heat seal strength,pin hole resistance, transparency and impact strength, making such filmsuitable for premium packaging applications. However, Shibata et al. donot disclose films with high ultimate hot tack strengths (i.e., values≧2.56 N/cm) and analysis of the data disclosed in the Examples providedby Shibata et al. reveals the properties of such film, particularly heatsealability, are additive and vary linearly with respect to thedensities of blended component polymers.

U.S. Pat. No. 4,981,760 to Naito et al. discloses a polyethylene mixturehaving a density of from 0.900 to 0.930 g/cc and melt flow rate of from0.1 to 100 g/10 in., which comprises (I) from 60 to 99 parts by weightof an ethylene-α-olefin random copolymer comprising ethylene and anα-olefin having from 4 to 10 carbon atoms, the copolymer having anα-olefin content of from 2.0 to 10 mol % and a density of from 0.895 to0.915 g/cc, the programmed-temperature thermogram of said copolymer asdetermined with a differential scanning calorimeter after beingcompletely melted and then gradually cooled showing an endothermic peakin a range of from 75° to 100° C., with the ratio of an endotherm atsaid peak to the total endotherm being at least 0.8, and (II) from 1 to40 parts by weight of high-density polyethylene having a density of atleast 0.945 g/cc, the programmed-temperature thermogram of saidhigh-density polyethylene as determined with a differential scanningcalorimeter after being completely melted and allowed to cool showing anendothermic peak at 125° C., or higher, wherein the sum of (I) and (II)amounts to 100 parts by weight. The component polymer (I) is said to bemanufactured using a vanadium catalyst and the film allegedly hasimproved heat sealability and hot tack. Naito et al. do not disclosethat the mixture is useful for fabricating molded articles, and inparticular, do not disclose that the mixture has high heat resistivitywhile simultaneously having good flexibility. Nor do Naito et al.disclose fabricated film comprising a component polymer (II) with adensity less than 0.945 g/cc. Moreover, where Naito et al. do describe afilm having a lower heat seal or hot tack initiation temperature, suchfilm is only obtained when the lower density component polymer (I)concentration is high (i.e., ≧85 parts) which is conventionally expectedto result in lower Vicat softening points and reduced heat resistivity.

U.S. Pat. No. 5,206,075 to Hodgson et al. discloses a multilayer heatsealable film comprising a base layer and a heat sealable layersuperimposed on one or both sides of the base layer. As the base layer,Hodgson discloses a blend of: (a) an olefin polymer having a densitygreater than 0.915 g/cc; and (b) a copolymer of ethylene and a C₃ -C₂₀alpha-monoolefin, with the copolymer (b) having a density of from about0.88 to about 0.915 g/cc, a melt index of from about 0.5 to about 7.5dg/min, a molecular weight distribution of no greater than about 3.5,and a composition distribution breadth index greater than about 70percent. As the heat sealable layer, Hodgson discloses a layercomprising a copolymer as defined in (b) with respect to the base layer.Hodgson does not disclose the use of a blend, such as that employed inthe base layer (a), as a suitable sealing layer and the preferred olefinpolymer for component (a) of the base layer is a copolymer of propylenewith about 1-10 mole percent ethylene.

The compositions disclosed by Shibata et al., Naito et al. and Hodgsonet al. are disadvantageous in that they are not optimally designed forpremium food packaging and storage container applications. Inparticular, there is a need for polymer compositions characterized by aVicat softening point which is greater than the heat seal initiationtemperature and/or hot tack initiation temperature of a thin film (i.e.,a film having a thickness in the range of about 0.25 to about 3 mils(0.006 to about 0.076 mm)) fabricated from the resin, to allow higherpackaging lines speeds without sacrificing the heat resistivity requiredfor such applications as, for example, cook-in and hot fill packaging.There is also a need for polymer compositions which have low levels ofn-hexane extractives, i.e., less than 15 weight percent, preferably lessthan 10 weight percent, more preferably less than 6 weight percent, mostpreferably less than 3 weight percent, as such compositions would beuseful in direct food contact applications. Those in industry wouldfurther find great advantage in polymer compositions which have theabove properties, as well as a controllably high modulus (indicatinggood dimensional stability and enabling high line speeds in verticalform, fill and seal applications) and high dart impact, tear resistance,and puncture resistance (leading to strong films and coatings,particularly useful in packaging articles containing sharp objects, suchas bones found in primal and subprimal cuts of meat). There is also aneed for polymer compositions that show a controllably low modulus andhigh heat resistance as molded articles as such, for instance, easy openfreezer-to-microwave food container lids.

SUMMARY OF THE INVENTION

Accordingly, the subject invention provides a polymer mixturecomprising:

(A) from 15 to 60 weight percent, based on the total weight of themixture, of at least one first ethylene polymer which is a substantiallylinear ethylene polymer having a density in the range of 0.850 to 0.920g/cc, wherein the substantially linear ethylene polymer is furthercharacterized as having

i. a melt flow ratio, I₁₀ /I₂ ≧5.63,

ii. a molecular weight distribution, M_(w) /M_(n), as determined by gelpermeation chromatography and defined by the equation: (M_(w)/M_(n))≦(I₁₀ /I₂)-4.63,

iii. a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene polymer and the linear ethylene polymercomprise the same comonomer or comonomers, the linear ethylene polymerhas an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene polymer andthe linear ethylene polymer are measured at the same melt temperatureusing a gas extrusion rheometer, and

iv. a single differential scanning calorimetry, DSC, melting peakbetween -30° and 150° C.; and

(B) from 40 to 85 weight percent, based on the total weight of themixture, of at least one second ethylene polymer which is ahomogeneously branched, heterogeneously branched linear, or non-shortchain branched linear ethylene polymer having a density in the range of0.890 to 0.965 g/cc;

wherein the polymer mixture is characterized as having a density of from0.890 to 0.930 g/cc, a differential between the densities of the firstethylene polymer and the second ethylene polymer of at least 0.015 g/cc,and a percent residual crystallinity, PRC, as defined by the equation:

    PRC≧5.0195×10.sup.4 (ρ)-2.7062×10.sup.4 (ρ).sup.2 -2.3246×10.sup.4,

where ρ is the density of the polymer mixture in grams/cubiccentimeters.

The subject invention further provides a polymer mixture comprising:

(A) from 15 to 60 weight percent, based on the total weight of themixture, of at least one first ethylene polymer which is a substantiallylinear ethylene polymer having a density in the range of 0.850 to 0.920g/cc, wherein the substantially linear ethylene polymer is furthercharacterized as having

i. a melt flow ratio, I₁₀ /I₂ ≧5.63,

ii. a molecular weight distribution, M_(w) /M_(n), as determined by gelpermeation chromatography and defined by the equation: (M_(w)/M_(n))≦(I₁₀ /I₂)-4.63,

iii. a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene polymer and the linear ethylene polymercomprise the same comonomer or comonomers, the linear ethylene polymerhas an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene polymer andthe linear ethylene polymer are measured at the same melt temperatureusing a gas extrusion rheometer, and

iv. a single differential scanning calorimetry, DSC, melting peakbetween -30° and 150° C.; and

(B) from 40 to 85 weight percent, based on the total weight of themixture, of at least one second ethylene polymer which is ahomogeneously branched, heterogeneously branched linear, or non-shortchain branched linear ethylene polymer having a density between 0.890and 0.942 g/cc;

wherein the polymer mixture is characterized as having a density of from0.890 to 0.930 g/cc, and a differential between the densities of thefirst ethylene polymer and the second ethylene polymer of at least 0.015g/cc, Vicat softening point of at least 75° C.; and

wherein

(a) a 0.038 mm thick film sealant layer fabricated from the polymermixture has a heat seal initiation temperature equal to or less than100° C. and an ultimate hot tack strength equal to or greater than 2.56N/cm, and

(b) the Vicat softening point of the polymer mixture is more than 6° C.higher than the heat seal initiation temperature of the film sealantlayer.

The subject invention further provides a polymer mixture comprising:

(A) from 15 to 60 weight percent, based on the total weight of themixture, of at least one first ethylene polymer which is a substantiallylinear ethylene polymer having a density in the range of 0.850 to 0.900g/cc, wherein the substantially linear ethylene polymer is furthercharacterized as having

i. a melt flow ratio, I₁₀ /I₂ ≧5.63,

ii. a molecular weight distribution, M_(w) /M_(n), as defined by theequation: (M_(w) /M_(n))≦(I₁₀ /I₂)-4.63,

iii. a gas extrusion rheology such that the critical shear rate at onsetof surface melt fracture for the substantially linear ethylene polymeris at least 50 percent greater than the critical shear rate at the onsetof surface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene polymer and the linear ethylene polymercomprise the same comonomer or comonomers, the linear ethylene polymerhas an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene polymer andthe linear ethylene polymer are measured at the same melt temperatureusing a gas extrusion rheometer,

iv. a single differential scanning calorimetry, DSC, melting peakbetween -30° and 150° C.; and

v. a n-hexane extractive level of substantially 100 weight percent basedon the weight of the first ethylene polymer; and

(B) from 40 to 85 weight percent, based on the total weight of themixture, of at least one second ethylene polymer which is ahomogeneously branched, heterogeneously branched linear, or non-shortchain branched linear ethylene polymer having a density in the range of0.890 to 0.942 g/cc;

wherein the polymer mixture is characterized as having a density of from0.890 to 0.930 g/cc, a differential between the densities of the firstethylene polymer and the second ethylene polymer of at least 0.015 g/ccand a compositional hexane-extractive level which is at least 30 percentlower than the expected extractive amount based on the total weight ofthe mixture.

The subject invention further provides any of the polymer mixtures asdefined herein in the form of a fabricated film, film layer, coating ormolded article for such uses as cook-in bags, pouches for flowablematerials, barrier shrink films, injected molded lids and packaging filmsealant layers.

These and other embodiments will be more fully described in the DetailedDescription set forth below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plot of percent residual crystallinity as a function ofdensity for Example and Comparative polymer mixtures and for singlecompositions of substantially linear ethylene polymers andheterogeneously branched linear ethylene polymers.

FIG. 2 is a plot of heat seal initiation temperature as a function ofVicat softening point in °C. for Example and Comparative polymermixtures and for single polymer compositions of substantially linearethylene polymers and heterogeneously branched linear ethylene polymers.

FIG. 3 is a plot of hot tack initiation temperature in °C. as a functionof density in g/cc for Example and Comparative polymer mixtures and forsingle polymer compositions of substantially linear ethylene polymersand heterogeneously branched linear ethylene polymers.

FIG. 4 is a plot of hot tack initiation temperature in °C. as a functionof Vicat softening point in °C. for Example and Comparative polymermixtures and for single polymer compositions of substantially linearethylene polymers and heterogeneously branched linear ethylene polymers.

FIG. 5 is a graphical illustration of the proper alignment between aninitial, unexposed print of the edge configuration of an ASTM flex barand a subsequent bar print following exposure to an elevated oventemperature. The distance between the bar prints is taken as heat sag incentimeters for Examples.

FIG. 6 is a graphical illustration of a differential scanningcalorimetry (DSC) "first heat" melting curve which illustrates theportion of the curve above 100° C. that is actually quantified for 100°C. percent residual crystallinity determinations.

DEFINITIONS OF TERMS

The term "polymer", as used herein, refers to a polymeric compoundprepared by polymerizing monomers, whether of the same or a differenttype. The generic term polymer thus embraces the term "homopolymer",usually employed to refer to polymers prepared from only one type ofmonomer, and the term "interpolymer", as defined hereinafter.

The term "interpolymer", as used herein, refers to polymers prepared bythe polymerization of at least two different types of monomers. Thegeneric term "interpolymer" thus includes the term "copolymers", whichis usually employed to refer to polymers prepared from two differentmonomers, as well as to polymers prepared from more than two differenttypes of monomers.

The term "percent residual crystallinity", as used herein, refers to afirst heat differential scanning calorimetry (DSC) determination of thatamount of polymer material that melts at temperatures above 100° C. or110° C. The test method used to determine the percent residualcrystallinity of Examples is provided below.

The terms "controlled modulus" and "controllably low or high modulus",as used herein, refer to the ability to affect the modulus of a film,coating or molded article essentially independent of the heatresistivity of the polymer mixture or the heat seal initiationtemperature of a sealant layer made from the polymer mixture byspecifying ("controlling") the final density of the mixture.

The term "expected extractive amount", as used herein, refers to theadditive weight percent of n-hexane extractives expected based on theweight fraction calculation for the individual n-hexane extractivelevels contributed by the first and second ethylene polymers of apolymer mixture. As an example of the calculation, where a polymermixture comprises (I) 30 weight percent of a first ethylene polymerwhich has a n-hexane extractive level of 50 weight percent, and (II) 70weight percent of a second ethylene polymer which has a n-hexaneextractive level of 10 weight percent, the polymer mixture will have anexpected extractive amount of 22 weight percent where 15 weight percentwould be contributed by the first ethylene polymer and 7 weight percentwould be contributed by the second ethylene polymer.

The term "compositional hexane extractive level", as used herein, refersto the total weight percent of n-hexane extracted from an Example inaccordance with the test method set forth in 21 CFR 177.1520 (d)(3)(ii).

The term "heat seal initiation temperature", as used herein, refers tothe minimum temperature at which a 0.038 mm thick film sealant layer ofa nylon/adhesive/sealant coextruded film structure measures a heat sealstrength of at least 0.4 kg/cm when folded over and sealed to itself.The test method used to determine the heat seal initiation temperatureof Examples, including the description of the coextruded film structureused, is provided herein below.

The term "ultimate hot tack strength", as used herein, refers to themaximum hot tack strength of a 0.038 mm thick film sealant layer in anylon/adhesive/sealant coextruded structure. The test method used todetermine the ultimate hot tack strength of Examples is provided hereinbelow.

DETAILED DESCRIPTION OF THE INVENTION

The first ethylene polymer of the mixture of the invention, Component(A), is described as at least one substantially linear ethylene polymerhaving a density in the range of 0.850 to 0.920 g/cc. When used tofabricate the film and coating of the invention, the first ethylenepolymer will have a density of greater than 0.865 g/cc, preferablygreater than 0.875 g/cc, more preferably greater than 0.880 g/cc. Whenused to fabricate the film and coating of the invention, the firstethylene polymer will also have a density of less than 0.920 g/cc,preferably less than 0.910 g/cc, more preferably less than 0.900 g/cc.When used to fabricate the molded article of the invention, for purposesof, but not limited to, maximizing heat resistivity, the first ethylenepolymer will have a density less than 0.890 g/cc, preferably less than0.875 g/cc, more preferably less than 0.870 g/cc.

When the first ethylene polymer has a density of less than 0.900 g/cc,it will be further characterized as having a n-hexane extractive levelof substantially 100 weight percent based on the weight of the firstethylene polymer. When the first ethylene polymer has a density lessthan 0.850 g/cc, it becomes tacky and difficult to handle indry-blending operations. For the fabricated film and coating of theinvention, when the first ethylene polymer has a density greater than0.920 g/cc, heat seal and hot tack properties will be undesirablyreduced. Also for the fabricated film and coating of the invention, whenthe density of the first ethylene polymer is less than 0.865 g/cc, theVicat softening point will be undesirably low. For the molded article ofthe invention, when the first ethylene polymer has a density greaterthan 0.890 g/cc, undesirably, the heat resistivity of the mixture willbe lower.

The second ethylene polymer of the polymer mixture of the invention,Component (B), is described as at least one homogeneously branched,heterogeneously branched linear, or non-short chain branched linearethylene polymer having a density in the range of 0.890 to 0.965 g/cc.As such, suitable ethylene polymers are contemplated to includehomogeneously branched linear ethylene interpolymers, heterogeneouslybranched linear ethylene interpolymers (both of the preceding includepolymer classes known as linear low density polyethylene (LLDPE), mediumdensity polyethylene (MDPE), copolymer high density polyethylene (HDPE)and ultra low or very low density polyethylene (ULDPE or VLDPE)),substantially linear ethylene polymers, homopolymer high densitypolyethylene (HDPE) (referred to herein as "non-short chain branchedlinear"), and combinations thereof.

When used to fabricate the film and coating of the invention, the secondethylene polymer will have a density greater than 0.890 g/cc, preferablygreater than 0.900 g/cc, more preferably greater than 0.910 g/cc. Whenused to fabricate the film and coating of the invention, the secondethylene polymer will also have a density of less than 0.942 g/cc,preferably less than 0.940 g/cc, more preferably less than 0.938 g/cc.At densities greater than 0.942 g/cc, the differential between the Vicatsoftening point of the mixture (which is considered herein to be thesame for a film fabricated from the mixture) and the heat sealinitiation temperature of a 0.038 mm thick coextruded sealant layer isundesirably low (i.e., ≦6° C.). When the density of the second ethylenepolymer is less than 0.890 g/cc, the compositional hexane extractivelevel of the mixture is undesirably high.

When used to fabricate the molded article of the invention, the secondethylene polymer will have a density of at least 0.930 g/cc, preferablyof at least 0.950 g/cc, more preferably of at least 0.960 g/cc.

For direct food contact applications, preferably the second ethylenepolymer will be further characterized as having a n-hexane extractivelevel of no more than 10 weight percent, preferably no more than 6weight percent based on the weight of the second ethylene polymer.

The terms "homogeneous" and "homogeneously branched" are used in theconventional sense in reference to an ethylene polymer in which thecomonomer is randomly distributed within a given polymer molecule andwherein substantially all of the polymer molecules have the sameethylene to comonomer molar ratio. Homogeneously branched polymers arecharacterized by a short chain branching distribution index (SCBDI)greater than or equal to 30 percent, preferably greater than or equal to50 percent, more preferably greater than or equal to 90 percent. TheSCBDI is defined as the weight percent of the polymer molecules having acomonomer content within 50 percent of the median total molar comonomercontent. The SCBDI of polyolefins can be determined by well-knowntemperature rising elution fractionation techniques, such as thosedescribed by Wild et al., Journal of Polymer Science, Poly. Phys. Ed.,Vol. 20, p. 441 (1982), L. D. Cady, "The Role of Comonomer Type andDistribution in LLDPE Product Performance," SPE Regional TechnicalConference, Quaker Square Hilton, Akron, Ohio, October 1-2, pp. 107-119(1985), or U.S. Pat. No. 4,798,081, the disclosures of all which areincorporated herein by reference.

The term "substantially linear" means that, in addition to the shortchain branches attributable to homogeneous comonomer incorporation, theethylene polymer is further characterized as having long chain branchesin that the polymer backbone is substituted with an average of 0.01 to 3long chain branch/1000 carbons. Preferred substantially linear polymersfor use in the invention are substituted with from 0.01 long chainbranch/1000 carbons to 1 long chain branch/1000 carbons, and morepreferably from 0.05 long chain branch/1000 carbons to 1 long chainbranches/1000 carbons.

Long chain branching is defined herein as a chain length of at least 6carbons, above which the length cannot be distinguished using ¹³ Cnuclear magnetic resonance spectroscopy. The long chain branch can be aslong as about the same length as the length of the polymer backbone towhich it is attached.

The presence of long chain branching can be determined in ethylenehomopolymers by using ¹³ C nuclear magnetic resonance (NMR) spectroscopyand is quantified using the method described by Randall (Rev. Macromol.Chem. Phys., C29, V. 2&3, p. 285-297), the disclosure of which isincorporated herein by reference.

As a practical matter, current ¹³ C nuclear magnetic resonancespectroscopy cannot determine the length of a long chain branch inexcess of six carbon atoms. However, there are other known techniquesuseful for determining the presence of long chain branches in ethylenepolymers, including ethylene/1-octene interpolymers. Two such methodsare gel permeation chromatography coupled with a low angle laser lightscattering detector (GPC-LALLS) and gel permeation chromatographycoupled with a differential viscometer detector (GPC-DV). The use ofthese techniques for long chain branch detection and the underlyingtheories have been well documented in the literature. See, e.g., Zimm,G. H. and Stockmayer, W. H., J. Chem. Phys., 17, 1301 (1949) and Rudin,A., Modern Methods of Polymer Characterization, John Wiley & Sons, NewYork (1991) pp. 103-112, both of which are incorporated by reference.

A. Willem deGroot and P. Steve Chum, both of The Dow Chemical Company,at the Oct. 4, 1994 conference of the Federation of Analytical Chemistryand Spectroscopy Society (FACSS) in St. Louis, Mo., presented datademonstrating that GPC-DV is a useful technique for quantifying thepresence of long chain branches in substantially linear ethyleneinterpolymers. In particular, deGroot and Chum found that the level oflong chain branches in substantially linear ethylene homopolymer samplesmeasured using the Zimm-Stockmayer equation correlated well with thelevel of long chain branches measured using ¹³ C NMR.

Further, deGroot and Chum found that the presence of octene does notchange the hydrodynamic volume of the polyethylene samples in solutionand, as such, one can account for the molecular weight increaseattributable to octene short chain branches by knowing the mole percentoctene in the sample. By deconvoluting the contribution to molecularweight increase attributable to 1-octene short chain branches, deGrootand Chum showed that GPC-DV may be used to quantify the level of longchain branches in substantially linear ethylene/octene copolymers.

deGroot and Chum also showed that a plot of Log(I₂, Melt Index) as afunction of Log(GPC Weight Average Molecular Weight) as determined byGPC-DV illustrates that the long chain branching aspects (but not theextent of long branching) of substantially linear ethylene polymers arecomparable to that of high pressure, highly branched low densitypolyethylene (LDPE) and are clearly distinct from ethylene polymersproduced using Ziegler-type catalysts such as titanium complexes andordinary homogeneous catalysts such as hafnium and vanadium complexes.

For ethylene/alpha-olefin interpolymers, the long chain branch is longerthan the short chain branch that results from the incorporation of thealpha-olefin(s) into the polymer backbone. The empirical effect of thepresence of long chain branching in the substantial linearethylene/alpha-olefin interpolymers used in the invention is manifestedas enhanced rheological properties which are quantified and expressedherein in terms of gas extrusion rheometry (GER) results and/or meltflow, I₁₀ /I₂, increases.

In contrast to the term "substantially linear", the term "linear" meansthat the polymer lacks measurable or demonstrable long chain branches,i.e., the polymer is substituted with an average of less than 0.01 longbranch/1000 carbons.

Substantially linear ethylene interpolymers are further characterized ashaving

(a) a melt flow ratio, I₁₀ /I₂ ≧5.63,

(b) a molecular weight distribution, M_(w) /M_(n), as determined by gelpermeation chromatography and defined by the equation: (M_(w)/M_(n))≦(I₁₀ /I₂)-4.63,

(c) a critical shear stress at the onset of gross melt fracture, asdetermined by gas extrusion rheometry, of greater than 4×10⁶ dynes/cm²,or

a gas extrusion rheology such that the critical shear rate at onset ofsurface melt fracture for the substantially linear ethylene polymer isat least 50 percent greater than the critical shear rate at the onset ofsurface melt fracture for a linear ethylene polymer, wherein thesubstantially linear ethylene polymer and the linear ethylene polymercomprise the same comonomer or comonomers, the linear ethylene polymerhas an I₂, M_(w) /M_(n) and density within ten percent of thesubstantially linear ethylene polymer and wherein the respectivecritical shear rates of the substantially linear ethylene polymer andthe linear ethylene polymer are measured at the same melt temperatureusing a gas extrusion rheometer, and

(d) a single differential scanning calorimetry, DSC, melting peakbetween -30° and 150° C.

Determination of the critical shear rate and critical shear stress inregards to melt fracture as well as other rheology properties such as"rheological processing index" (PI), is performed using a gas extrusionrheometer (GER). The gas extrusion rheometer is described by M. Shida,R. N. Shroff and L. V. Cancio in Polymer Engineering Science, Vol. 17,No. 11, p. 770 (1977), and in "Rheometers for Molten Plastics" by JohnDealy, published by Van Nostrand Reinhold Co. (1982) on pp. 97-99, bothof which are incorporated by reference herein in their entirety. GERexperiments are performed at a temperature of 190° C., at nitrogenpressures between 250 to 5500 psig using a 0.0754 mm diameter, 20:1 L/Ddie with an entrance angle of 180°. For the substantially linearethylene polymers described herein, the PI is the apparent viscosity (inkpoise) of a material measured by GER at an apparent shear stress of2.15×10⁶ dyne/cm². The substantially linear ethylene polymer for use inthe invention includes ethylene interpolymers and homopolymers and havea PI in the range of 0.01 kpoise to 50 kpoise, preferably 15 kpoise orless. The substantially linear ethylene polymers used herein have a PIless than or equal to 70 percent of the PI of a linear ethylene polymer(either a Ziegler polymerized polymer or a linear uniformly branchedpolymer as described by Elston in U.S. Pat. No. 3,645,992) having an I₂,M_(w) /M_(n) and density, each within ten percent of the substantiallylinear ethylene poylmers.

The rheological behavior of substantially linear ethylene polymers canalso be characterized the Dow Rheology Index (DRI), which expresses apolymer's "normalized relaxation time as the result of long chainbranching." (See, S. Lai and G. W. Knight ANTEC '93 Proceedings, INSITE™Technology Polyolefins (ITP)--New Rules in the Structure/RheologyRelationship of Ethylene α-Olefin Copolymers, New Orleans, La., May1993, the disclosure of which is incorporated herein by reference). DRIvalues range from 0 for polymers which do not have any measurable longchain branching (e.g., Tafmer™products available from MitsuiPetrochemical Industries and Exact™ products available from ExxonChemical Company) to about 15 and is independent of melt index. Ingeneral, for low to medium pressure ethylene polymers (particularly atlower densities) DRI provides improved correlations to melt elasticityand high shear flowability relative to correlations of the sameattempted with melt flow ratios. For the substantially linear ethylenepolymers useful in this invention, DRI is preferably at least 0.1, andespecially at least 0.5, and most especially at least 0.8. DRI can becalculated from the equation:

    DRI=(3652879*τ.sub.O 1.00649/η.sub.O -1)/10

where τ_(O) is the characteristic relaxation time of the material andη_(O) is the zero shear viscosity of the material. Both τ_(O) and η_(O)are the "best fit" values to the Cross equation, i.e.,

    η/η.sub.O =1/(1+(γ*τ.sub.O).sup.1-n)

where n is the power law index of the material, and η and γ are themeasured viscosity and shear rate, respectively. Baseline determinationof viscosity and shear rate data are obtained using a RheometricMechanical Spectrometer (RMS-800) under dynamic sweep mode from 0.1 to100 radians/second at 160° C. and a Gas Extrusion Rheometer (GER) atextrusion pressures from 1,000 psi to 5,000 psi (6.89 to 34.5 MPa),which corresponds to shear stress from 0.086 to 0.43 MPa, using a 0.0754mm diameter, 20:1 L/D die at 190° C. Specific material determinationscan be performed from 140° to 190° C. as required to accommodate meltindex variations.

An apparent shear stress versus apparent shear rate plot is used toidentify the melt fracture phenomena and quantify the critical shearrate and critical shear stress of ethylene polymers. According toRamamurthy in the Journal of Rheology, 30(2), 337-357, 1986, thedisclosure of which is incorporated herein by reference, above a certaincritical flow rate, the observed extrudate irregularities may be broadlyclassified into two main types: surface melt fracture and gross meltfracture.

Surface melt fracture occurs under apparently steady flow conditions andranges in detail from loss of specular film gloss to the more severeform of "sharkskin." Herein, as determined using the above-describedGER, the onset of surface melt fracture (OSMF) is characterized at thebeginning of losing extrudate gloss at which the surface roughness ofthe extrudate can only be detected by 40× magnification. The criticalshear rate at the onset of surface melt fracture for the substantiallylinear ethylene interpolymers and homopolymers is at least 50 percentgreater than the critical shear rate at the onset of surface meltfracture of a linear ethylene polymer having essentially the same I₂ andM_(w) /M_(n).

Gross melt fracture occurs at unsteady extrusion flow conditions andranges in detail from regular (alternating rough and smooth, helical,etc.) to random distortions. For commercial acceptability to maximizethe performance properties of films, coatings and moldings, surfacedefects should be minimal, if not absent. The critical shear stress atthe onset of gross melt fracture for the substantially linear ethylenepolymers, especially those having a density >0.910 g/cc, used in theinvention is greater than 4×10⁶ dynes/cm². The critical shear rate atthe onset of surface melt fracture (OSMF) and the onset of gross meltfracture (OGMF) will be used herein based on the changes of surfaceroughness and configurations of the extrudates extruded by a GER.Preferably, the substantially linear ethylene polymer will becharacterized by its critical shear rate when used as the first ethylenepolymer of the invention and by its critical shear stress when used asthe second ethylene polymer of the invention.

The substantially linear ethylene polymers used in the invention arealso characterized by a single DSC melting peak. The single melting peakis determined using a differential scanning calorimeter standardizedwith indium and deionized water. The method involves 5-7 mg samplesizes, a "first heat" to about 140° C. which is held for 4 minutes, acool down at 10°/min. to -30° C. which is held for 3 minutes, and heatup at 10° C./min. to 140° C. for the "second heat". The single meltingpeak is taken from the "second heat" heat flow vs. temperature curve.Total heat of fusion of the polymer is calculated from the area underthe curve.

For polymers having a density of 0.875 g/cc to 0.910 g/cc, the singlemelting peak may show, depending on equipment sensitivity, a "shoulder"or a "hump" on the low melting side that constitutes less than 12percent, typically, less than 9 percent, and more typically less than 6percent of the total heat of fusion of the polymer. Such an artifact isobservable for other homogeneously branched polymers such as Exact™resins and is discerned on the basis of the slope of the single meltingpeak varying monotonically through the melting region of the artifact.Such an artifact occurs within 34° C., typically within 27° C., and moretypically within 20° C. of the melting point of the single melting peak.The heat of fusion attributable to an artifact can separately determinedby specific integration of its associated area under the heat flow vs.temperature curve.

The substantially linear ethylene polymers are analyzed by gelpermeation chromatography (GPC) on a Waters 150 high temperaturechromatographic unit equipped with differential refractometer and threecolumns of mixed porosity. The columns are supplied by PolymerLaboratories and are commonly packed with pore sizes of 10³, 10⁴, 10⁵and 10⁶ Å. The solvent is 1,2,4-trichlorobenzene, from which 0.3 percentby weight solutions of the samples are prepared for injection. The flowrate is 1.0 milliliters/minute, unit operating temperature is 140° C.and the injection size is 100 microliters.

The molecular weight determination with respect to the polymer backboneis deduced by using narrow molecular weight distribution polystyrenestandards (from Polymer Laboratories) in conjunction with their elutionvolumes. The equivalent polyethylene molecular weights are determined byusing appropriate Mark-Houwink coefficients for polyethylene andpolystyrene (as described by Williams and Ward in Journal of PolymerScience, Polymer Letters, Vol. 6, p. 621, 1968) to derive the followingequation:

    M.sub.polyethylene =a*(M.sub.polystyrene).sup.b.

In this equation, a=0.4316 and b=1.0. Weight average molecular weight,M_(w), is calculated in the usual manner according to the followingformula: M_(w) =Σw_(i) ×M_(i), where w_(i) and M_(i) are the weightfraction and molecular weight, respectively, of the i^(th) fractioneluting from the GPC column.

Substantially linear ethylene polymers are known to have excellentprocessability, despite having a relatively narrow molecular weightdistribution (i.e., the M_(w) /M_(n) ratio is typically less than 3.5,preferably less than 2.5, and more preferably less than 2). Moreover,unlike homogeneously and heterogeneously branched linear ethylenepolymers, the melt flow ratio (I₁₀ /I₂) of substantially linear ethylenepolymers can be varied essentially independently of the molecular weightdistribution, M_(w) /M_(n). Accordingly, the first ethylene polymer,Component (A), of the inventive polymer mixtures is a substantiallylinear ethylene polymer. In addition to having enhanced rheologicalproperties, at least one substantially linear ethylene polymer is usedin the invention as the first ethylene polymer for purposes ofproviding, but not limited to, high ultimate hot tack strength, i.e.,≧6.5 N/inch (2.56 N/cm).

Substantially linear ethylene polymers are homogeneously branchedethylene polymers and are disclosed in U.S. Pat. No. 5,272,236 and U.S.Pat. No. 5,272,272, the disclosures of which are incorporated herein byreference. Homogeneously branched substantially linear ethylene polymersare available from The Dow Chemical Company as Affinity™ polyolefinplastomers, and as Engage™ polyolefin elastomers. Homogeneously branchedsubstantially linear ethylene polymers can be prepared via the solution,slurry, or gas phase polymerization of ethylene and one or more optionalalpha-olefin comonomers in the presence of a constrained geometrycatalyst, such as is disclosed in European Patent Application 416,815-A,incorporated herein by reference. Preferably, a solution polymerizationprocess is used to manufacture the substantially linear ethyleneinterpolymer used in the present invention.

Homogeneously branched linear ethylene polymers have long beencommercially available. As exemplified in U.S. Pat. No. 3,645,992 toElston, homogeneously branched linear ethylene polymers can be preparedin conventional polymerization processes using Ziegler-type catalystssuch as, for example, zirconium and vanadium catalyst systems. U.S. Pat.No. 4,937,299 to Ewen et al. and U.S. Pat. No. 5,218,071 to Tsutsui etal. disclose the use of metallocene catalysts, such as catalyst systemsbased on hafnium, for the preparation of homogeneously branched linearethylene polymers. Homogeneously branched linear ethylene polymers aretypically characterized as having a molecular weight distribution, M_(w)/M_(n), of about 2. Commercial examples of homogeneously branched linearethylene polymers include those sold by Mitsui Petrochemical Industriesas Tafmer™ resins and by Exxon Chemical Company as Exact™ resins.

The terms "heterogeneous" and "heterogeneously branched" mean that theethylene polymer is characterized as a mixture of interpolymer moleculeshaving various ethylene to comonomer molar ratios. Heterogeneouslybranched ethylene polymers are characterized as having a short chainbranching distribution index (SCBDI) less than about 30 percent.Heterogeneously branched linear ethylene polymers are available from TheDow Chemical Company as Dowlex™ linear low density polyethylene and asAttane™ ultra-low density polyethylene resins. Heterogeneously branchedlinear ethylene polymers can be prepared via the solution, slurry or gasphase polymerization of ethylene and one or more optional alpha-olefincomonomers in the presence of a Ziegler Natta catalyst, by processessuch as are disclosed in U.S. Pat. No. 4,076,698 to Anderson et al.,incorporated herein by reference. Preferably, heterogeneously branchedethylene polymers are typically characterized as having molecular weightdistributions, M_(w) /M_(n), in the range of from 3.5 to 4.1.

The ethylene polymers useful as component (A) or (B) of the mixtures ofthe invention can independently be interpolymers of ethylene and atleast one alpha-olefin. Suitable alpha-olefins are represented by thefollowing formula:

    CH.sub.2 ═CHR

where R is a hydrocarbyl radical. The comonomer which forms a part ofcomponent (A) may be the same as or different from the comonomer whichforms a part of component (B) of the inventive mixture.

Further, R may be a hydrocarbyl radical having from one to twenty carbonatoms. Suitable alpha-olefins for use as comonomers in a solution, gasphase or slurry polymerization process or combinations thereof include1-propylene, 1-butene, 1-isobutylene, 1-pentene, 1-hexene,4-methyl-1-pentene, 1-heptene and 1-octene, as well as other monomertypes such as styrene, halo- or alkyl-substituted styrenes,tetrafluoro-ethylene, vinyl benzocyclobutane, 1,4-hexadiene,1,7-octadiene, and cycloalkenes, e.g., cyclopentene, cyclohexene andcyclooctene. Preferably, the alpha-olefin will be 1-butene, 1-pentene,4-methyl-1-pentene, 1-hexene, 1-heptene, 1-octene, or mixtures thereof.More preferably, the alpha-olefin will be 1-hexene, 1-heptene, 1-octene,or mixtures thereof, as films fabricated with the resultantinterpolymers will have especially improved puncture resistance, dartimpact, and tear strength properties where such higher alpha-olefins areutilized as comonomers. However, most preferably, the alpha-olefin willbe 1-octene.

The polymer mixture of the invention will have a density of from 0.890to 0.930 g/cc as measured in accordance with ASTM D792. Further, thepolymer mixture of the invention will have a density of at least 0.890g/cc, preferably of at least 0.903 g/cc, more preferably of at least0.909 g/cc. The polymer mixture of the invention will have a density ofless than 0.930 g/cc, preferably less than 0.928 g/cc, more preferablyof less than 0.922 g/cc.

For the inventive polymer mixture, the difference between the densitiesof the first and second polymer is generally at least 0.015 g/cc,preferably, at least 0.025 g/cc, more preferably at least 0.045 g/cc.For purposes of the molded article of the invention, the densitydifferential can be even higher such as at least 0.065 g/cc, especiallyat least 0.085 g/cc. In general, the higher the density differential,the more improved the heat resistance will be relative to aheterogeneously branched linear ethylene polymer having essentially thesame density and, as such, higher density differentials are particularlypreferred for the molded articles of the invention.

The polymer mixture comprises from 15 to 60 weight percent, preferablyfrom 15 to 50, more preferably from 20 to 45 weight percent of the firstethylene polymer (A) based on the total weight of the mixture and from40 to 85 weight percent, preferably from 50 to 85, more preferably from55 to 80 weight percent at the second ethylene polymer (B) based on thetotal weight of the mixture.

Component (A) and component (B) will be independently characterized byan I₂ melt index of from 0.01 to 100 g/10 min. In preferred embodiments,components (A) and (B) will be independently characterized by an I₂ meltindex of from 0.1 to 50 g/10 minutes. By "independently characterized"it is meant that the I₂ melt index of component (A) need not be the sameas the I₂ melt index of component (B).

The I₂ of the polymer mixture of the invention will be from 0.01 to 100g/10 min., preferably from 0.1 to 75 g/10 min., more preferably from 0.5to 50 g/10 min. Generally, for polymer mixtures useful in preparing thefabricated film of the invention, the I₂ will be less than 30 g/10 min.,preferably less than 20 g/10 min., more preferably less than 15 g/10min. Generally, for polymer mixtures useful in preparing the moldedarticle of the invention, the I₂ of the polymer mixture will be greaterthan 10 g/10 min., preferably greater than 15 g/10 min., more preferablygreater than 20 g/10 min.

The polymer mixture of the invention is generally characterized ashaving a percent residual crystallinity, PRC, as defined by theequation:

    PRC≧5.0195×10.sup.4 (ρ)-2.7062×10.sup.4 (ρ).sup.2 -2.3246×10.sup.4,

preferably

    PRC≧5.7929×10.sup.4 (ρ)-3.1231×10.sup.4 (ρ).sup.2 -2.6828×10.sup.4,

more preferably

    PRC≧6.4363×10.sup.4 (ρ)-3.470×10.sup.4 (ρ).sup.2 -2.9808×10.sup.4,

In the equations immediately above, ρ is the density of the polymermixture in grams/cubic centimeters.

One preferred polymer mixture of the invention will be characterized ashaving a percent residual crystallinity which is at least 17.5% higher,preferably at least 20% higher, more preferably at least 35% higher,most preferably at least 50% higher than the percent residualcrystallinity of a single linear ethylene polymer, or alternately, of alinear ethylene polymer mixture (i.e., a polymer mixture whereinessentially all component polymers are "linear"), having essentially thesame density.

A plot of percent residual crystallinity of the polymer mixture of theinvention as a function of density (FIG. 1), will show a maximum percentresidual crystallinity value for polymer mixtures characterized by adensity in the range of 0.890 to 0.930 g/cc.

Where a polymer mixture of the invention is not defined by one of theabove equations or the mixture does not have a percent residualcrystallinity at least equal to or higher than the percent residualcrystallinity a linear ethylene polymer (or linear ethylene polymermixture) having essentially the same density, such inventive polymermixture will be distinguished by its enhanced performance in the form ofmonolayer or coextruded film, or alternately, such mixture will comprisea first ethylene polymer which has a n-hexane extractive level ofsubstantially 100 weight percent and the polymer mixture will be furthercharacterized as having a compositional hexane extractive level of lessthan 30 percent, preferably less than 40 percent, more preferably lessthan 50 percent, especially less than 80 percent, most especially lessthan 90 percent lower than the expected extractive amount for themixture based on the total weight of the mixture.

A preferred polymer mixture of the invention will be characterized ashaving a compositional hexane extractive level of less than 15 percent,preferably less than 10 percent, more preferably less than 6, mostpreferably less than 3 percent based on the total weight of the mixture.

Temperature rising elution fractionation (TREF) such as described byWild et al. can be used to "fingerprint" or identify the novel mixturesof the invention.

Another preferred polymer mixture of the invention will be characterizedby a Vicat softening point of at least 75° C., preferably at least 85°C., and more preferably at least 90° C.

In another embodiment, a preferred polymer mixture of the invention,when fabricated as a 1.5 mil (0.038 mm) thick sealant layer of anylon/adhesive/sealant blown coextruded film, will be characterized by aheat seal initiation temperature of less than 100° C., preferably lessthan 90° C., more preferably less than 85° C., most preferably less than80° C.

In another embodiment, a preferred polymer mixture of the invention willhave a Vicat softening point more than 6° C. higher, preferably at leastthan 8° C. higher, more preferably at least 10° C. higher, especially atleast 15° C. higher, most especially at least 20° C. higher than theheat seal initiation temperature of a 1.5 mil (0.038 mm) thick sealantlayer (fabricated from the polymer mixture) of a nylon/adhesive/sealantblown coextruded film.

In another embodiment, a polymer mixture of the invention, when moldedinto an essentially flat part having a thickness of 125 mils (31.7 mm),will be (characterized as having a microwave warp distortion of lessthan 0.75 cm, preferably less than 0.70 cm and most preferably less thanor equal to 0.65 cm while maintaining a flexural modulus of less than35,000 psi, preferably less than 30,000 psi, more preferably less than25,000 psi (172.4 MPa).

A preferred molded article of the invention will show a heat resistivitysuperior to a linear ethylene polymer having a density of 0.927 g/ccwhile simultaneously showing a controllably low flexural modulus, thatis, having a flexural modulus lower than a linear ethylene polymerhaving a density less than 0.927 g/cc, preferably less than 0.920 g/cc,more preferably less than 0.912 g/cc.

Another embodiment of the present invention is a process for fabricatingthe polymer mixture of the invention into the form of a film, filmlayer, coating or molded article. The process can include a laminationand coextrusion technique or combinations thereof, or using the polymermixture alone, and includes a blown film, cast film, extrusion coating,injection molding, blow molding, compression molding, rotomolding, orinjection blow molding operation or combinations thereof.

The polymer mixture of the invention can be formed by any convenientmethod, including dry blending the individual components andsubsequently melt mixing in a mixer or by mixing the components togetherdirectly in a mixer (e.g., a Banbury mixer, a Haake mixer, a Brabenderinternal mixer, or a single or twin screw extruder including acompounding extruder and a side-arm extruder employed directly downstream of a interpolymerization process.

The mixtures of the invention can further be formed in-situ via theinterpolymerization of ethylene and the desired alpha-olefin using aconstrained geometry catalyst in at least one reactor and a constrainedgeometry catalyst or a Ziegler-type catalyst in at least one otherreactor. The reactors can be operated sequentially or in parallel. Anexemplary in-situ interpolymerization process is disclosed in PCT PatentApplication 94/01052, incorporated herein by reference.

The polymer mixture of the invention can further be formed by isolatingcomponent (A) from a heterogeneous ethylene polymer by fractionating theheterogeneous ethylene polymer into specific polymer fractions with eachfraction having a narrow branching distribution, selecting the fractionsappropriate to meet the limitations specified for component (A), andblending the selected fraction in the appropriate amounts with acomponent (B). This method is obviously not as economical as the in-situpolymerization described above, but can nonetheless be used to obtainthe polymer mixture of the invention.

Additives, such as antioxidants (e.g., hindered phenolics, such asIrganox™ 1010 or Irganox™ 1076 supplied by Ciba Geigy), phosphites(e.g., Irgafos™ 168 also supplied by Ciba Geigy), cling additives (e.g.,PIB), Standostab PEPQ™ (supplied by Sandoz), pigments, colorants,fillers, and the like may also be included in the polymer mixture of thepresent invention or in films formed from the same. Although generallynot required, films, coatings and moldings formed from the polymermixture of the present invention may also contain additives to enhanceantiblocking, mold release and coefficient of friction characteristicsincluding, but not limited to, untreated and treated silicon dioxide,talc, calcium carbonate, and clay, as well as primary, secondary andsubstituted fatty acid amides, release agents, silicone coatings, etc.Still other additives, such as quaternary ammonium compounds alone or incombination with ethylene-acrylic acid (EAA) copolymers or otherfunctional polymers, may also be added to enhance the antistaticcharacteristics of films, coatings and moldings formed from the polymermixture of the invention and permit the use of these polymer mixturesin, for example, the heavy-duty packaging of electronically sensitivegoods.

The polymer mixture of the invention may further include recycled andscrap materials and diluent polymers, to the extent that the desiredperformance properties are maintained. Exemplary diluent materialsinclude, for example, elastomers, rubbers and anhydride modifiedpolyethylenes (e.g., polybutylene and maleic anhydride grafted LLDPE andHDPE) as well as with high pressure polyethylenes such as, for example,low density polyethylene (LDPE), ethylene/acrylic acid (EAA)interpolymers, ethylene/vinyl acetate (EVA) interpolymers andethylene/methacrylate (EMA) interpolymers, and combinations thereof.

The polymer mixture of the invention may find utility in a variety ofapplications, including but not limited to shrink film (including butnot limited to barrier shrink film), packages formed via horizontal orvertical form/fill/seal machinery, cook-in packaged foods, injectionmolded containers (particularly food storage containers), etc.

Barrier shrink film refers to oriented films (typically biaxiallyoriented films) which are caused to shrink about the packaged articleupon the application of heat. Barrier shrink films find utility in thepackaging of primal and subprimal cuts of meat, ham, poultry, bacon,cheese, etc. A typical barrier-shrink film utilizing the polymer mixtureof the invention may be a three to seven layer co-extruded structure,with a heat sealing food contact layer (such as the polymer mixture ofthe invention), an outer layer (such as heterogeneously branched linearlow density or ultra-low density polyethylene), and a barrier layer(such as a vinylidene chloride polymer or copolymer) interposed between.Adhesion promoting tie layers (such as Primacor™ ethylene-acrylic acid(EAA) copolymers available from The Dow Chemical Company, and/orethylene-vinyl acetate (EVA) copolymers, as well as additionalstructural layers (such as Affinity™ polyolefin plastomers, Engage™polyolefin elastomers, both available from The Dow Chemical Company,ultra-low density polyethylene, or blends of any of these polymers witheach other or with another polymer, such as EVA) may be optionallyemployed. Barrier shrink films so fabricated with the mixtures of theinvention will preferably shrink at least 25 percent in both the machineand transverse directions. Film or film layers fabricated from thepolymer mixture of the invention are particularly well-suited as sealantlayers in multilayer food packaging structures such as barrier shrinkfilm and aseptic packages.

Cook-in packaged foods are foods which are prepackaged and then cooked.The packaged and cooked foods go directly to the consumer, institution,or retailer for consumption or sale. A package for cook-in must bestructurally capable of withstanding exposure to cook-in time andtemperature conditions while containing a food product. Cook-in packagedfoods are typically employed for the packaging of ham, turkey,vegetables, processed meats, etc.

Vertical form/fill/seal packages are typically utilized for thepackaging of flowable materials, such as milk, wine, powders, etc. In avertical form/fill/seal (VFFS) packaging process, a sheet of the plasticfilm structure is fed into a VFFS machine where the sheet is formed intoa continuous tube by sealing the longitudinal edges of the film togetherby lapping the plastic film and sealing the film using an inside/outsideseal or by fin sealing the plastic film using an inside/inside seal.Next, a sealing bar seals the tube transversely at one end to form thebottom of a pouch. The flowable material is then added to the formedpouch. The sealing bar then seals the top end of the pouch and eitherburns through the plastic film or a cutting device cuts the film, thusseparating the formed completed pouch from the tube. The process ofmaking a pouch with a VFFS machine is generally described in U.S. Pat.Nos. 4,503,102 and 4,521,437, the disclosures of which are incorporatedherein by reference.

As stated above, in one embodiment, the polymer mixture of the inventionwill be characterized by a Vicat softening point of at least 75° C.,more preferably of at least 85°, most preferably of at least 90° C. Asfurther stated above, in one embodiment, the polymer mixture of theinvention, when fabricated into a 1.5 mils (0.038 mm) blown coextrudedfilm as a sealant layer having a thickness of, will further becharacterized by a heat seal initiation temperature of less than 100°C., preferably less than 90° C., more preferably less than 85° C., mostpreferably less than 80° C.

As further stated above, in one embodiment, the polymer mixture of theinvention will be characterized by a Vicat softening point which is morethan 6° C., preferably equal to or more than 8° C., more preferablyequal to or more than 10° C., especially equal to or more than 15° C.,most especially equal to or more than 20° C. higher than the heat sealinitiation temperature of a 1.5 mil (0.038 mm) thick sealant layer(fabricated from the inventive polymer mixture) of anylon/adhesive/sealant blown coextruded film.

As also stated above, in one embodiment, an essentially flat molded partfabricated from the polymer mixture of the invention will becharacterized by having less than 0.75 cm, preferably less than 0.70 cm,and more preferably less than 0.65 cm of microwave warp distortion whenexposed to low frequency microwave radiation energy for 5 minutes andwhile showing a flexural modulus of less than 35,000 psi (241.3 MPa)prior to microwave exposure.

One particular embodiment of the polymer mixture of the invention,especially suitable as a food packaging resin, when fabricated into ablown monolayer film having a thickness of 2 mils (0.051 mm), will becharacterized as having a controllable 2% secant modulus (MD) in therange of 5,000 psi (34 MPa) to 35,000 psi (241 MPa), especially in therange of 7,000 psi (48 MPa) to 25,000 psi (172 MPa).

Another particular embodiment of the polymer mixture of the invention,especially suitable as a food packaging resin, when fabricated into ablown monolayer film having a thickness of 2 mil (0.051 mm), will becharacterized by an Elmendorf tear (MD) of at least 300 g, preferably atleast 600 g, and more preferably at least 800 g.

Another particular embodiment of the polymer mixture of the invention,especially suitable as a food packaging resin, when fabricated into ablown monolayer film having a thickness of 2 mil (0.051 mm), will becharacterized by a Dart Impact (Type B) of greater than 300 g,preferably greater than 450 g, more preferably greater than 500 g, andmost preferably greater than 600 g.

Another particular embodiment of the polymer mixture of the invention,especially suitable as a food packaging resin, when fabricated into ablown monolayer film having a thickness of 2 mil (0.051 mm), will becharacterized by a puncture resistance of greater than 150 ft-lb/in³(126 kg-cm/cc), preferably greater than 200 ft-lb/in³ (168 kg-cm/cc),more preferably greater than 250 ft-lb/in³ (210 kg-cm/cc), morepreferably at least 275-ft lb/in³ (231 kg-cm/cc), and most preferably atleast 300 ft-lb/in³ (252 kg-cm/cc).

DESCRIPTION OF TEST METHODS

Densities are measured in accordance with ASTM D-792 and are reported asgrams/cubic centimeter (g/cc). The measurements reported in the Examplesbelow are determined after the polymer samples have been annealed for 24hours at ambient conditions.

Melt index measurements are performed according to ASTM D-1238,Condition 190° C./2.16 kilogram (kg) and condition 190° C./5 kg whichare known as I₂ and I₅, respectively. For purposes of this invention, incalculating certain values in the Examples, I₅ and I₂ values roughlyrelate to one another by a factor of about 5.1; for example, a 1.0 I₂index melt is equivalent to a 5.1 I₅ melt index. Melt index is inverselyproportional to the molecular weight of the polymer. Thus, the higherthe molecular weight, the lower the melt index, although therelationship is not linear. Melt index is reported as g/10 minutes. Meltindex determinations can also be performed with even higher weights,such as in accordance with ASTM D-1238, Condition 190° C./10 kg, whichis known as I₁₀.

The term "melt flow ratio" as defined herein in the conventional senseas the ratio of a higher weight melt index determination to a lowerweight melt index determination. For measured I₁₀ and I₂ melt indexvalues, the melt flow ratio is conveniently designated as I₁₀ /I₂.

The Elmendorf tear values of films prepared from the mixtures of theinvention is measured in accordance with ASTM D1922 and is reported ingrams. Elmendorf tear is measured both the machine direction (MD) and inthe cross direction (CD). The term "tear strength" is used herein torepresent the average between MD and CD Elmendorf tear values and,likewise, is reported in grams. The dart impact of films prepared fromthe mixtures of the invention is measured in accordance with ASTM D1709.Where indicated and according to the relationship of higher thicknessesyield increased performance values, Elmendorf tear and dart impactresults are normalized to exactly 2 mils (0.051 mm) by proportionateincreases or decreases based on actual measured (micrometer) filmthickness. Such normalization calculations are only performed andreported where thickness variations are less than 10 percent, i.e.,where the measured thickness is in the range of about 1.8-2.2 mils(0.46-0.56 mm).

Film puncture values are obtained using an Instron tensiometer equippedwith a strain cell and an integrated digital display that provides forcedeterminations. A single ply of a blown monolayer film having athickness of 2 mils (0.051 mm) is mounted taut between the two halves ofa circular holder constructed of aluminum and machined to couple thehalves securely when they are joined together. The exposed film areawhen mounted in the holder is 4 inches (10.2 cm) in diameter. The holderis then affixed to the upper stationary jaw of the tensiometer. To thelower jaw of the tensiometer which is set to traverse upwardly, ahemispherical aluminum probe having a 12.5 mm diameter is affixed. Theprobe is aligned to traverse upwards through the center of the mountedfilm at a deformation rate of 250 mm/min. The force required to rupturethe film is taken from the digital display and divided by the filmthickness and the diameter of the probe to provide puncture resistancein kg-cm/cc.

Secant modulus is measured in accordance with ASTM D882 on 2 mil (0.051mm) blown monolayer film fabricated from the Examples, the n-hexaneextractive level is measured in accordance with 21 CFR 177.1520(d)(3)(ii) on 4-mil (1-mm) compression molded film fabricated from theExamples, and the Vicat softening point is measured in accordance withASTM D1525 on 2 mil (0.051 mm) blown monolayer film fabricated from theExamples.

Heat seal initiation temperature is defined as the minimum temperaturefor a 2 lb/in (0.4 kg/cm) seal strength. Heat seal testing is performedusing a 3.5 mil (0.089 mm) thick coextruded film of the followingstructure: 1 mil (0.025 mm) Capron Xtraform™ 1590F Nylon 6/6, 6copolymer available from Allied Chemical Company/1 mil (0.025 mm)Primacor™ 1410 ethylene-acrylic acid (EAA) copolymer available from TheDow Chemical Company/1.5 mil (0.038 mm) sealant layer of the polymermixture of the Examples. The testing is done on a Topwave Hot TackTester using a 0.5 second dwell time with a 40 psi (0.28 MPa) seal barpressure. The seals are made at 5° increments in the range of 60°-160°C. by folding the sealant layer over and sealing it to itself. Theso-formed seals are pulled 24 hours after they are made using an Instrontensiometer at a 10 in/min. (51 cm/min.) crosshead rate.

Hot tack initiation temperature is defined as the minimum sealtemperature required to develop a 4 Newton/in (1.6 N/cm) seal strength.Hot tack testing is also performed using above-described three-layercoextruded structure and a Topwave Hot Tack Tester set at a 0.5 seconddwell, 0.2 second delay time, and 40 psi (0.28 MPa) seal bar pressure.Hot tack seals are made at 5° increments in the temperature range of60°-160° C. by folding the sealant layer over and hot tack sealing it toitself. The peel rate applied to the so-formed hot tack seals is of 150mm/sec. The tester pulls the seal immediately after the 0.2 seconddelay. Ultimate hot tack strength is taken as the maximum N/cm value inthe 60°-160° C. temperature range for the Example.

Residual crystallinity is determined using a Perkin-Elmer DSC 7. Thedetermination involves quantifying the heat of fusion of that portion ofan Example above 100° C. or 110° C. at first heat. The area under "firstheat" melting curve is determined by computer integration usingPerkin-Elmer PC Series Software Version 3.1. FIG. 6 graphicallyillustrates a "first heat" melting curve and the area under the curveabove 100° C. actually integrated.

The ASTM test methods, as well as the test method promulgated by theFood and Drug Administration for hexane-extractive levels set forth in21 CFR 177.1520 (d)(3)(ii), are incorporated herein by reference.

EXAMPLES

The following examples are provided for the purpose of explanation,rather than limitation.

Examples 1-3

Example 1 is prepared using an in-situ polymerization and mixtureprocess, such as is disclosed in PCT Patent Application No. 94/01052,the disclosure of which is incorporated herein by reference. Theparticular production details are set forth as follows.

Constrained Geometry Catalyst Preparation

A known weight of the constrained-geometry organometallic complex((CH₃)₄ C₅))--(CH₃)₂ Si--N--(t-C₄ H₉)!Ti(CH₃)₂ is dissolved in Isopar™ Ehydrocarbon (available from Exxon Chemical Company) to give a clearsolution with a titanium (Ti) concentration of 9.6×10⁻⁴ M. A similarsolution of the activator complex tris(perfluorophenyl)borane (3.8×10⁻³M) is also prepared. A known weight of methylalumoxane (available fromTexas Alkyls as MMAO) is dissolved in n-heptane to give a solution withan MMAO concentration of 1.06×10⁻² M. These solutions are independentlypumped such that they are combined just prior to being fed into thefirst polymerization reactor and such that the constrained geometrycatalyst, the activator complex, and the MMAO are in a molar ratio of1:3.5:7.

Heterogeneous Catalyst Preparation

A heterogeneous Ziegler-type catalyst is prepared substantiallyaccording to the procedure of U.S. Pat. No. 4,612,300 (Example P), bysequentially adding to a volume of Isopar™ E hydrocarbon, a slurry ofanhydrous magnesium chloride in Isopar™ E hydrocarbon, a solution ofEtAlCl₂ in n-hexane, and a solution of Ti(O-iPr)₄ in Isopar™ Ehydrocarbon, to yield a slurry containing a magnesium concentration of0.166M and a ratio of Mg/Al/Ti of 40.0:12.5:3.0. An aliquot of thisslurry and a dilute solution of Et₃ Al (TEA) are independently pumpedwith the two streams being combined just prior to introduction into thesecond polymerization reactor to give an active catalyst with a finalTEA:Ti molar ratio of 6.2:1.

Polymerization process

Ethylene is fed into a first reactor at a rate of 40 lb/hr (18.2 kg/hr).Prior to introduction into the first reactor, the ethylene is combinedwith a diluent mixture comprising Isopar™ E hydrocarbon (available fromExxon Chemical Company) and 1-octene. With respect to the firstpolymerization reactor, the 1-octene:ethylene ratio (constituting freshand recycled monomer) is 0.28:1 (mole percent) and the diluent:ethylenefeed ratio is 8.23:1 (weight percent). A homogeneous constrainedgeometry catalyst and cocatalyst such as prepared above is introducedinto the first polymerization reactor. The catalyst, activator, and MMAOflow rates into the first polymerization reactor are 1.64×10⁻⁵ lbs.Ti/hr (7.4×10⁻⁶ kg Ti/hr), 6.21×10⁻⁴ lbs. activator/hr (2.82×10⁻⁴ kgactivator/hr), and 6.57×10⁻⁵ lbs. MMAO/hr (3.0×10⁻⁵ kg MMAO/hr),respectively. The polymerization is conducted at a reaction temperaturein the range of 70°-160° C.

The reaction product of the first polymerization reactor is transferredto a second reactor. The ethylene concentration in the exit stream fromthe first polymerization reactor is less than four percent, indicatingthe presence of long chain branching as described in U.S. Pat. No.5,272,236.

Ethylene is further fed into a second polymerization reactor at a rateof 120 lbs./hr (54.5 kg/hr). Prior to introduction into the secondpolymerization reactor, the ethylene and a stream of hydrogen arecombined with a diluent mixture comprising Isopar™ E hydrocarbon and1-octene. With respect to the second polymerization reactor, the1-octene:ethylene feed ratio (constituting fresh and recycled monomer)is 0.196:1 (mole percent), the diluent:ethylene ratio is 5.91:1 (weightpercent), and the hydrogen:ethylene feed ratio is 0.24:1 (mole percent).A heterogeneous Ziegler catalyst and cocatalyst as prepared above areintroduced into the second polymerization reactor. The catalyst (Ti) andcocatalyst (TEA) concentrations in the second polymerization reactor are2.65×10⁻³ and 1.65×10⁻³ molar, respectively. The catalyst and cocatalystflow rates into the second polymerization reactor are 4.49×10⁻⁴ lbs.Ti/hr (2.04×10⁻⁴ kg Ti/hr) and 9.14×10⁻³ lbs. TEA/hr (4.15×10⁻³ kgTEA/hr) respectively. The polymerization is conducted at a reactiontemperature in the range of 130°-200° C. The conversion and productionsplit between the first and second polymerization reactors is such as toyield the "percent of mixture" value for Example 1 set forth in Table 1.

To the resulting polymer, a standard catalyst kill agent (1250 ppmCalcium Stearate) and antioxidants (200 ppm Irganox™ 1010, i.e.,tetrakis methylene3-(3,5-di-tert-butyl-4-hydroxy-phenylpropionate)!methane, available fromCiba-Geigy and 800 ppm Sandostab™ PEPQ, i.e.,tetrakis-(2,4-di-tert-butyl-phenyl)-4,4' biphenylphosphonite, availablefrom Sandoz Chemical) are added to stabilize the polymer. Although theCalcium Stearate is known to conventionally function as a processingaid, comparative experiments will show it does not contribute to theenhanced rheological properties of the substantially linear polymersuseful in the invention.

The polymer mixtures of Examples 2 and 3 are prepared in a similarfashion. The split between the first and second polymerization reactorsis such as to yield the "percent of mixture" values set forth in Table1.

The densities, melt indices, and hexane extractive levels of the firstreactor products, the second reactor products, and the resultantin-reactor mixtures as well as the Vicat softening point, densitydifferential between the component polymers and expected n-hexaneextractive amount of the in-reactor mixtures are further set forth inTable 1.

Examples 4-8 and Comparative Examples 9-13

The mixtures of Examples 4-8 are prepared by dry blending thesubstantially linear ethylene polymer component (A) and theheterogeneously branched linear ethylene polymer component (B) (or inthe case of Example 5, the substantially linear ethylene polymercomponent (B)) in a lab scale mechanical tumble blender. ComparativeExamples 9-11 are also prepared using the mechanical tumble blender. Thecomponent weight percentages based on the total weight of the respectivepolymer mixtures are set forth in Table 1. With respect to theindividual component polymers, component (A) for Comparative Example 11is a linear ethylene/1-butene copolymer commercially available fromMitsui Petrochemical Industries under the designation of Tafmer™ A4085.For Examples 4-8 and Comparative Examples 9-10, the substantially linearethylene polymer component (A) and component (B) in the case of Example5, is prepared by techniques disclosed in U.S. Pat. No. 5,272,236 via asolution ethylene/1-octene interpolymerization process utilizing a((CH₃)₄ C₅))--(CH₃)₂ Si--N--(t-C₄ H₉)!Ti(CH₃)₂ activated withtris(perfluorophenyl)borane and MMAO. To the resulting polymer, astandard catalyst kill agent and antioxidants described above are addedto stabilize the polymer.

The heterogeneously branched components (B) of Examples 4-8 andComparative Examples C9-C11 are solution-polymerized copolymers ofethylene and 1-octene manufactured with the use of a Ziegler titaniumcatalyst system. To the resulting polymers, Calcium Stearate, inquantities sufficient for functioning as a standard processing aid andas a catalyst kill agent, and as antioxidants, 200 ppm Irganox™ 1010 and1600 ppm Irgafos™ 168, a phosphite stabilizer available from Ciba-Geigy,are added to stabilize the polymer and to enhance its rheologicalproperties. Comparative Examples C12 and C13 are single polymercompositions in contrast to the above inventive and comparative polymermixtures. Comparative Example C12 is a substantially linearethylene/1-octene copolymer also prepared by techniques disclosed inU.S. Pat. No. 5,272,236 utilizing a ((CH₃)₄ C₅))--(CH₃)₂ Si--N--(t-C₄H₉)!Ti(CH₃)₂ activated with tris(perfluorophenyl)borane and MMAO. To theresulting polymer, calcium stearate as a catalyst kill agent andantioxidants as described above for Example 1 are added to stabilize thepolymer. Comparative Example C13 is a heterogeneously branched linearethylene/1-octene copolymer prepared in a solution process utilizing aZiegler titanium catalyst system. The melt index of component (B) ofComparative Example C9 and the resultant mixture are reported as acorrected I₂ value using the correction factor discussed above. Thecomponent (B) second ethylene polymer of Comparative Example 9 has ameasured I₅ melt index of 0.26 g/10 minutes which has been corrected to0.05 g/10 min.

The densities, melt indices, and n-hexane extractive level of thecomponent polymers, resultant polymer mixtures and single polymercompositions as well as the Vicat softening point, density differentialbetween the component polymers and the expected n-hexane extractiveamount of the mixtures are set forth in Table 1.

                                      TABLE 1                                     __________________________________________________________________________    Example       1      2      3      4      5      6                            __________________________________________________________________________    First Polymer Type                                                                          Substantially                                                                        Substantially                                                                        Substantially                                                                        Substantially                                                                        Substantially                                                                        Substantially                Ethylene      Linear Linear Linear Linear Linear Linear                       Polymer                                                                             Density (g/cc)                                                                        0.887  0.88   0.888  0.887  0.887  0.887                              I.sub.2 (g/10 min)                                                                    1.0    5.0    0.6    0.5    0.5    0.5                                n-Hexane                                                                              100    100    100    100    100    100                                Extractives                                                                   Percent of                                                                            20     28     42     20     50     50                                 Mixture (wt %)                                                          Second                                                                              Polymer Type                                                                          Hetero-                                                                              Hetero-                                                                              Hetero-                                                                              Hetero-                                                                              Substantially                                                                        Hetero-                      Ethylene      geneously                                                                            geneously                                                                            geneously                                                                            geneously                                                                            Linear geneously                    Polymer       Branched                                                                             Branched                                                                             Branched                                                                             Branched      Branched                                   Linear Linear Linear Linear        Linear                             Density (g/cc)                                                                        0.920  0.925  0.926  0.920  0.902  0.912                              I.sub.2 (g/10 min)                                                                    1.0    1      1.4    1.0    1.0    1.0                                n-Hexane                                                                              <2     <2     <2     <2     <2     <2                                 Extractives (%)                                                               Percent of                                                                            80     72     58     80     50     50                                 Mixture (wt %)                                                          Polymer                                                                             Density (g/cc)                                                                        0.912  0.912  0.912  0.913  0.894  0.899                        Mixture                                                                             First/Second                                                                          0.033  0.045  0.038  0.033  0.015  0.025                              Polymer                                                                       Density                                                                       Differential                                                                  (g/cc)                                                                        I.sub.2 (g/10 min)                                                                    1.05   1.5    1.0    1.0    0.7    0.7                                n-Hexane                                                                              0.8    0.8    0.7    ND     2.5    4.3                                Extractives (%)                                                               Expected                                                                              21.6   29.4   43.2   21.6   51.0   51.0                               n-Hexane                                                                      Extractives (%)                                                               Percent Lower                                                                         96.3   97.3   98.4   NA     95.2   91.6                               Than Expected                                                                 Extractive                                                                    Amount                                                                        Vicat   91.9   94.6   91.85  98.3   76.1   76.15                              Softening Point                                                               (VSP) (°C.)                                                      __________________________________________________________________________    Example       7     8     C9    C10   C11   C12   C13                         __________________________________________________________________________    First Polymer Type                                                                          Substantially                                                                       Substantially                                                                       Substantially                                                                       Substantially                                                                       Homo- None  Substantially               Ethylene      Linear                                                                              Linear                                                                              Linear                                                                              Linear                                                                              geneously   Linear                      Polymer                               Branched                                                                      Linear                                        Density (g/cc)                                                                        0.887 0.896 0.887 0.871 0.881 NA    0.920                             I.sub.2 (g/10 min)                                                                    0.5   1.3   0.5   0.87  3.5   NA    1.0                               n-Hexane                                                                              100   100   100   100   100   NA    <2                                Extractives (%)                                                               Percent of                                                                            20    50    30    35    20    0     100                               Mixture (wt %)                                                          Second                                                                              Polymer Type                                                                          Hetero-                                                                             Hetero-                                                                             Hetero-                                                                             Hetero-                                                                             Hetero-                                                                             Hetero-                                                                             None                        Ethylene      geneously                                                                           geneously                                                                           geneously                                                                           geneously                                                                           geneously                                                                           geneously                         Polymer       Branched                                                                            Branched                                                                            Branched                                                                            Branched                                                                            Branched                                                                            Branched                                        LInear                                                                              Linear                                                                              Linear                                                                              Linear                                                                              Linear                                                                              Linear                                  Density (g/cc)                                                                        0.935 0.935 0.942 0.920 0.920 0.912 NA                                I.sub.2 (g/10 min)                                                                    1.0   1.0   0.05  1.0   1.0   1.0   NA                                n-Hexane                                                                              <2.0  <2.0  <2.0  <2.0  <2.0  2.3   NA                                Extractives (%)                                                               Percent of                                                                            80    50    70    65    80    100   0                                 Mixture (wt %)                                                          Polymer                                                                             Density (g/cc)                                                                        0.925 0.917 0.926 0.903 0.912 0.912 0.920                       Mixture                                                                             First/Second                                                                          0.048 0.039 0.055 0.049 0.039 None  None                        or    Polymer Density                                                         Single                                                                              Differential                                                            Polymer                                                                             (g/cc)                                                                        I.sub.2 (g/10 min)                                                                    0.9   1.1   -0.2  1.0   1.3   1.0   1.0                               n-Hexane                                                                              0.3   ND    0.9   11.8  1.2   2.3   <2.0                              Extractives (%)                                                               Expected                                                                              21.6  NA    31.4  36.3  21.6  NA    NA                                n-Hexane                                                                      Extractives (%)                                                               Percent Lower                                                                         98.4  NA    97.1  67.4  94.3  NA    NA                                Than Expected                                                                 Extractive                                                                    Amount                                                                        Vicat Softening                                                                       113.15                                                                              95    109   64.6  99.05 96.1  108.7                             Point (VSP)(°C.)                                                 __________________________________________________________________________     ND denotes the measurement was not determined.                                NA denotes the measurement is not applicable.                            

As illustrated in Table 1, although the polyethylene mixtures ofExamples 1-8 contain at least 20 weight percent of a homogeneouslybranched substantially linear ethylene polymer component (A) which issubstantially fully soluble in hexane, the mixtures of the invention arecharacterized by a relatively low compositional hexane extractive level,i.e., less than 4.5 weight percent. Table 1 also illustrates that theactual n-hexane extractive level of inventive mixture is at least 30%and as high as 98% lower than the expected extractive amount for themixture. While not wishing to be bound by any particular theory, it isbelieved that the higher density, more crystalline ethylene polymer usedin the invention as component (B) creates a tortuous path and, as such,significantly reduces the amount of n-hexane extractable material thatwould otherwise traverse and escape the polymer mixture matrix.

Further, the polymer mixtures of Examples 1-8 are characterized by aVicat softening point greater than 75° C. Conversely, the Vicatsoftening point of Comparative Example C10 is too low for packagingapplications requiring improved heat resistivity. Additionally, althoughthe actual n-hexane extractive level of Comparative Example C10 issignificantly lower than its expected n-hexane extractive amount, itsactual n-hexane extractive level is still markedly higher (i.e., from2.7 to 39 times higher) than that of preferred polymer mixtures of theinvention. The deficiencies of Comparative Example C10 are thought to bedue to the relatively low density (i.e., 0.903 g/cc) of the mixture. Assuch, for film and coating of the invention, it is believed that wherethe density of the component (A) polymer is equal to or less than 0.870g/cc, the density of the component (B) polymer should be greater than0.920 g/cc (i.e., the density differential between the first and secondethylene polymers should be greater than 0.049 g/cc) but still less than0.942 g/cc.

Formation of Monolayer Films

The mixtures of Examples 1-8 and the single polymer compositions andmixtures of Comparative Examples C9-C13 are fabricated into a 2 mil(0.051 mm) thick monolayer blown (tubular) film at about 200° C. melttemperature using a 2.5 inch (6.4 cm) diameter, 30:1 L/D Gloucesterblown film line equipped with a 6 inch (15.2 cm) annular die. Themonolayer blown films are evaluated for 1% and 2% secant modulus,Elmendorf tear, dart impact, and puncture resistance using theprocedures described above. The results of the evaluation are set forthin Table 2.

                                      TABLE 2                                     __________________________________________________________________________    Example   1   2   3   4   5   6   7   8   C9  C10 C11 C12 C13                 __________________________________________________________________________    Monolayer Film Performance Properties                                         2% Secant Modulus                                                                       22,000                                                                            22,147                                                                            18,870                                                                            19,541                                                                            6,595                                                                             8,989                                                                             33355                                                                             ND  41,887                                                                            12,597                                                                            20,278                                                                            18,361                                                                            25,325              (MD)      (152)                                                                             (153)                                                                             (130)                                                                             (135)                                                                             (45)                                                                              (62)                                                                              (230)   (289)                                                                             (87)                                                                              (140)                                                                             (127)                                                                             (175)               (psi) (MPa)                                                                   1% Secant Modulus                                                                       ND  ND  ND  21,522                                                                            7,627                                                                             10,421                                                                            37,516                                                                            ND  46,514                                                                            14,299                                                                            22,470                                                                            21,176                                                                            29,275              (MD)                  (148)                                                                             (53)                                                                              (72)                                                                              (259)   (321)                                                                             (99)                                                                              (155)                                                                             (146)                                                                             (202)               (psi) (MPa)                                                                   2% Secant Modulus                                                                       26,000                                                                            22,033                                                                            24,590                                                                            21,140                                                                            7,052                                                                             9,391                                                                             36,440                                                                            ND  48,964                                                                            12,758                                                                            22,725                                                                            19,160                                                                            25,863              (CD)      (179)                                                                             (152)                                                                             (170)                                                                             (146)                                                                             (49)                                                                              (65)                                                                              (251)   (338)                                                                             (88)                                                                              (157)                                                                             (132)                                                                             (178)               (psi) (MPa)                                                                   1% Secant Modulus                                                                       ND  ND  ND  22,993                                                                            8,492                                                                             10,898                                                                            37,238                                                                            ND  52,433                                                                            14,953                                                                            25,597                                                                            21,511                                                                            28,005              (CD)                  (159)                                                                             (59)                                                                              (75)                                                                              (257)   (362)                                                                             (103)                                                                             (176)                                                                             (148)                                                                             (193)               (psi) (MPa)                                                                   Elmendorf Tear                                                                          800 1,094                                                                             811 659 359 312 579 670 330 1,155                                                                             645 765 427                 (Type A) (MD)                                                                 (grams)                                                                       Elmendorf Tear                                                                          980 1,222                                                                             1,030                                                                             877 512 482 891 900 907 1,414                                                                             794 912 749                 (Type A) (CD)                                                                 (grams)                                                                       Dart Impact                                                                             512 646 850 698 >850                                                                              >850                                                                              323 ND  330 0   430 800 270                 (Type B) (grams)                                                              Puncture Resistance                                                                     300 259 320 312 255 254 193 290 142 213 292 142 176                 (ft-lbs/cc)                                                                   __________________________________________________________________________     ND denotes the measurement was not determined.                           

As illustrated in Table 2, the polymer mixtures of Examples 1-8 exhibita controllable 2% secant modulus (MD) as low as 6,595 psi in the case ofExample 5 and as high as 33,355 psi in the case of Example 7. Table 2also illustrates that the polymer mixtures of Examples 1-8 as well asthe comparative mixtures of C9-C13 are characterized by an Elmendorftear (MD) of at least 300 g, a Dart Impact (Type B) of at least 300 g,and a puncture resistance of at least 150 ft-lb/in³ (126 kg-cm/cc),establishing additional criteria of a food packaging resin.

Formation of Coextruded Films

The mixtures of Examples 1-8 and the single polymer compositions andmixtures of Comparative Examples C9-C13 are fabricated into a 3.5 mil(0.89 mm) thick coextruded film using a coextrusion blown film unitmanufactured by Egan Machinery equipped with two 30:1 L/D 2.5 inch (6.4cm) diameter extruders, one 30:1 L/D 2 inch (5.1 cm) extruder and an 8inch (20.3 cm) spiral mandrel annular die. The individual layers of thefilm are as follows: 1 mil (0.025 mm) nylon; 1 mil (0.025 mm) Primacor™1410 an ethylene-acrylic acid (EAA) copolymer available from The DowChemical Company); and 1.5 mil (0.038 mm) of Examples 1-8 or ComparativeExamples C9-C13. The resultant coextruded films are evaluated for heatseal initiation temperature, hot tack initiation temperature, andultimate hot tack strength. The results of the evaluation are set forthin Table 3.

                                      TABLE 3                                     __________________________________________________________________________    Example   1   2   3   4   5   6   7   8   C9  C10 C11 C12 C13                 __________________________________________________________________________    Coextruded Film Performance Properties                                        Heat Seal Initiation                                                                    81  71  76  77  63  65  98  87  116 54  73  103 108                 Temperature (°C.)                                                      Hot Tack Initiation                                                                     80  69  75  78  68  67  102 92  ˜110                                                                        48  80  108 109                 Temperature (°C.)                                                      Ultimate Hot Tack                                                                       7.3 7.2 11.8                                                                              7.4 7.1 7.9 9.7 6.6 3.8 10.0                                                                              6.1 8.2 9.4                 Strength  (2.87)                                                                            (2.83)                                                                            (4.64)                                                                            (2.91)                                                                            (2.79)                                                                            (3.11)                                                                            (3.83)                                                                            (2.60)                                                                            (1.48)                                                                            (3.94)                                                                            (2.40)                                                                            (3.23)                                                                            (3.70)              N/in (N/cm)                                                                   VSP - Heat Seal                                                                         10.9                                                                              23.6                                                                              15.9                                                                              21.3                                                                              13.1                                                                              11.2                                                                              15.2                                                                              8.0 -7.0                                                                              10.6                                                                              26.1                                                                              -6.9                                                                              0.7                 Initiation                                                                    Temperature (°C.)                                                      __________________________________________________________________________

Heat Sealability

As illustrated in Table 3, the polymer mixtures of Examples 1-8 exhibita heat seal initiation temperature of less than 100° C. and as low as63° C. as in the case of Example 5, and a differential between the Vicatsoftening point of the polymer mixture and the heat seal initiationtemperature of a 1.5 mil (0.038 mm) film layer fabricated of the polymermixture of at least 8° C. (as in the case of Examples 1-8), of at least10° C. (as in the case of Examples 1-7), of at least 15° C. (as in thecase of Examples 2-4, and 7), and of at least 20° C. (as in the case ofExamples 2 and 4). Comparative Examples C9, C12 and C13 all have heatseal and hot tack initiation temperatures that merely approximate theirrespective Vicat softening points. Table 3 also illustrates ComparativeExample C11 is also characterized by a desirably low heat seal and hottack initiation temperature and a desirably high differential betweenits Vicat softening point and its heat seal initiation temperature.

Regression Analysis

In another evaluation, the heat seat initiation temperatures of themixtures and single polymer compositions (as well as other singlecomposition illustrated in Table 4 and designated Comparative ExamplesC14-C19) are plotted as function of the Vicat softening point for thematerial. The individual relationships are subjected to first and secondorder linear regression analysis using Cricket Graph computer softwareVersion 1.3 supplied commercially by Cricket Software Company toestablish an equation for the respective relationships. FIG. 2illustrates the resulting equations and that, desirably, the heat sealinitiation temperature of a given inventive mixture is at least 13%lower in the case of Examples 1-8, at least 20% lower in the case ofExamples 1-6 and 8, and at least 25% lower in the case of Examples 2-6than a heterogeneously linear polymer having essentially the same Vicatsoftening point.

                                      TABLE 4                                     __________________________________________________________________________    Heterogeneous Linear Ethylene Polymers                                                             Heat Seal                                                                           Hot Tack                                                     Melt Index                                                                          Vicat                                                                              Initiation                                                                          Initiation                                                                          Vicat - Heat                                 Comparative                                                                         Density                                                                           (g/10 Softening                                                                          Temperature                                                                         Temperature                                                                         Seal                                         Example                                                                             (g/cc)                                                                            minutes)                                                                            Point (°C.)                                                                 (°C.)                                                                        (°C.)                                                                        Initiation                                   __________________________________________________________________________    C12   0.912                                                                             1.0   96   103   108   -7                                           C14   0.935                                                                             1.1   119  116   117   3                                            C15   0.920                                                                             1.0   105  111   109   -6                                           C16   0.905                                                                             0.80  83   87    103   -4                                           __________________________________________________________________________    Substantially Linear Ethylene Polymers                                                             Heat Seal                                                                           Hot Tack                                                     Melt Index                                                                          Vicat                                                                              Initiation                                                                          Initiation                                                                          Vicat - Heat                                 Comparative                                                                         Density                                                                           (g/10 Softening                                                                          Temperature                                                                         Temperature                                                                         Seal                                         Example                                                                             (g/cc)                                                                            min.) Point (°C.)                                                                 (°C.)                                                                        (°C.)                                                                        Initiation                                   __________________________________________________________________________    C13   0.920                                                                             1.0   108.7                                                                              108   109   0.7                                          C17   0.908                                                                             1.0   ND   91    99    NA                                           C18   0.902                                                                             1.0   89   83    88    6                                            C19   0.895                                                                             1.3   73   76    85    -3                                           __________________________________________________________________________    Ethylene Vinyl Acetate (EVA) Copolymers                                                            Heat Seal                                                                           Hot Tack                                                 Percent                                                                           Melt Index                                                                          Vicat                                                                              Initiation                                                                          Initiation                                                                          Vicat - Heat                                 Comparative                                                                         Vinyl                                                                             (g/10 Softening                                                                          Temperature                                                                         Temperature                                                                         Seal                                         Example                                                                             Acetate                                                                           min.) Point (°C.)                                                                 (°C.)                                                                        (°C.)                                                                        Initiation                                   __________________________________________________________________________    C20   12  0     79   86    None  -7                                                                      (strength was                                                                 below the                                                                     1.6 N/cm                                                                      threshold)                                         C21   18  0.80  65   80    None  -15                                                                     (strength was                                                                 below the                                                                     1.6 N/cm                                                                      threshold)                                         __________________________________________________________________________     ND denotes the measurement was not determined                            

Hot Tackability

In another evaluation, the hot tack initiation temperatures of themixtures and single polymer compositions (as well as other singlepolymer compositions illustrated in Table 4 and designated ComparativeExamples C14-C19) are plotted as function of the density and Vicatsoftening point for the material. In the same fashion as above, theseindividual relationships are subjected to first and second order linearregression analysis to establish an equation for the correspondingrelationship. FIGS. 3 and 4 illustrate the resulting equations and that,desirably, the hot tack initiation temperature of a given inventivemixture is at least 10% lower in the case of Examples 1-8, at least 20%lower in the case of Examples 1-6, and at least 30% lower in the case ofExamples 2-6 than a heterogeneously linear polymer having essentiallythe same density or Vicat softening point.

The low heat seal and hot tack initiation temperatures of the inventivemixtures permits industrial fabricators to increase productivity bymaking more seals per unit time and, as such, fabricating more bags,pouches, and other packages and containers that are produced by creatingheat seals. By having Vicat softening points several degrees higher thantheir respective heat seal initiation temperatures, the inventivepolymer mixtures will better maintain seal integrity during use inpackaging applications involving high temperatures (for example, about45° C.) such as hot-fill packaging where items are packaged hot anddropped onto bottom seals, cook-in applications and boil-in-bagapplications.

Table 3 further illustrates that the ultimate hot tack strength ofExamples 1-8 is greater than or equal to 6.5 N/in. (2.56 N/cm) and is ashigh as 11.8 N/in (4.65 N/cm) in the case of Example 3. The ultimate hotstrength of the comparative mixtures, including C11 which is exemplaryof the mixture disclosed by Shibata et al. in U.S. Pat. No. 4,429,079,are all less than 6.5 N/in (2.56 N/cm). The high ultimate hot tackstrength of the inventive mixture is particularly important in verticalform/fill/seal packaging applications where the items to be packaged aredropped into the package and onto the bottom hot tack seal immediatelyafter the seal is formed. High hot tack strength insures the bottom sealwill not rupture during loading of the items and, as such, will helpeliminate leakers and spillage of the items.

Vertical Form/Fill/Seal Machinability

In another evaluation, Example 2 is evaluated for its machinabilityperformance when processed through automated converting and packagingequipment. Good "machinability", as the term is used herein, refers tothe ability to convert film into non-filled packages on high speedpackaging equipment without generating packages that are outside of thedesired package specification or having premature equipment shutdowns.

Machinability is determined by first fabricating from Example 2 a 2.0mil (0.051 mm) thick monolayer film using the Gloucester blown film unitdescribed above. Then the film is run through a Hayssen Ultima Super CMBVertical Form/Fill/Seal (VFFS) machine for at least 5 minutes todetermine whether 7 inch wide×9.5 inch long (17.8 cm wide×24.1 cm long)pouches can be produced at a rate of 25 pouches/minute and at a higherrate of 50 pouches/minute. In this evaluation, the film fabricated fromExample 2 shows good machinability. Non-filled pouches within thedesired dimensional specification were prepared at the rates of 25 and50/minute without any equipment shutdowns.

For purposes of comparison, Comparative Example 21, which is an ethylenevinyl acetate (EVA) copolymer containing 18 weight percent vinyl acetateand having heat seal characteristics comparable to Example 2 (See, Table4), is also evaluated for VFFS non-filled packaging machinability.However, Comparative Example 21 experienced continuous equipmentinterruptions and shutdowns and could not be processed at a packagingspeed as low as 20 non-filled pouches per minute in this evaluation. Thepoor performance of Comparative Example 21 is attributable to itstackiness and low modulus (poor dimensional stability) which results inthe film excessively necking-down and dragging on the forming tube ofthe VFFS unit.

Cook-In Performance

In another evaluation, Example 2 is evaluated for its cook-inperformance by procedures pursuant to those disclosed in U.S. Pat. No.4,469,742, which is incorporated herein by reference. In thisevaluation, a 3.5 mil (0.89 mm) thick coextruded film consisting of 1.5mils (0.038 mm) of nylon/1.0 mil (0.25 mm) Primacor™ 1410/1.5 mils(0.038 mm) of Example 2 is fabricated using the Egan coextrusion linedescribed above. The nylon material, as for all othernylon/adhesive/sealant film structures used and disclosed herein, isCapron Xtraform™ 1590F Nylon 6/6, 6 copolymer supplied commercially byAllied Chemical Company. The Hayssen VFFS unit described above is alsoused in combination with a Pro/Fill 3000 Liquid Filler unit in thisevaluation. The temperature of the sealing bars and platen for makingbottom, top and side fin seals to prepare the pouches is set at 250° F.(121° C.). Using the coextruded film, 7 inch wide×9.5 inch long (17.8 cmwide×24.1 cm long) pouches are prepared and filled with 1,000milliliters of water on the VFFS unit at a rate of 15 filled pouches perminute. Five water filled and heat sealed pouches are collected andplaced into a large water-tight pan. The pan is then filled with water,covered with a suitable lid and placed in a Blue M forced-air convectionoven and permitted to stand for 17 hours at 85° C. After 17 hours ofoven time, the five pouches are removed from the oven and allowed tocool to ambient and inspect for seal integrity. In this evaluation, noleakers due to seal ruptures, delamination or cracking were detected.All five pouches fabricated from Example 2 passed this cook-inevaluation in accordance to criteria provided in U.S. Pat. No.4,469,742.

Shrink Response Evaluation

In another evaluation, a polymer mixture designated Example 22 isprepared by tumble blending, as component (A), 22 percent by weight ofthe total mixture of a substantially linear ethylene/1-octene copolymerhaving a density of 0.870 g/cc and produced according to techniquesdescribed in U.S. Pat. No. 5,272,236 and, as component (B), 78 percentby weight of the total mixture of a heterogeneously branchedethylene/1-octene copolymer having a density of 0.935 g/cc and producedusing a solution polymerization process and a Ziegler-type titaniumcatalyst. The mixture is then melt mixed on a 30 mm Werner-Pflieder ZSKco-rotating, twin screw extruder and pelletized. The mixture, which ischaracterized as having a density of 0.920 g/cc, is then extruded into200 mil (51 mm) thick sheet using a conventional cast film extruder unitequipped with a slot die and the melt temperature set at 415° F. (213°C.) and the chill roll set at 67° F. (19° C.). The resulting extrudedsheet is then cut into four 2 inch×2 inch (5.1 cm×5.1 cm) sheets andbiaxially stretched individually using a T. M. Long laboratorystretching frame. The sheets are stretched to a thickness of 1 mil(0.025 mm) using the various settings shown in Table 5 below.

                  TABLE 5                                                         ______________________________________                                        Stretch Temperature Setting                                                                  245° F. (118° C.),                                              top and bottom platens                                         Preheat Time   10 minutes                                                     Stretch Rate   5 in/min. (12.7 cm/min.)                                                      in both the machine and traverse directions                    Stretch Mode   Simultaneous Stretching                                        Stretch Ratio  4.5 × 4.5                                                ______________________________________                                    

After the biaxial stretching operation, the sheets are tested for freeshrinkage at 250° F. (121° C.) in accordance with ASTM D2732 andaveraged to determine the total shrink response. The average freeshrinkage of sheet fabricated from Example 21 measured 27 percent in themachine direction and 25 percent in the traverse direction. The mixturealso had an orientation temperature range of at least 11° C. which isbroader than that of typical homogeneously branched ethylene polymers.As such, Examples 1-8 and 22 are believed to be well-suited for use infabricating biaxially oriented films for use in such applications as,for example, barrier shrink packaging of primal and subprimal meat.

Fabrication of Molded Articles

In an injection molding evaluation, Examples 23-26 and ComparativeExamples C29-C31 are prepared by dry blending followed by melt mixing atabout 149° C. in a 1 inch (2.5 cm) diameter 24:1 L/D MPM extruder. Table6 provide a description of the component polymers as well the componentweight percentages expressed as "percent of mixture". The melt extrusionconditions for use in preparing Examples 23-26 and Comparative ExamplesC29-C31 are shown in Table 7. Examples 27 and 28 are prepared byoperating two polymerization reactors sequentially in a manner similarto that described for Example 1, utilizing reactor splits (conversionand production rates) that correspond to the percent of mixture in Table6.

Examples 23-28 are also compared to Comparative Examples C32 and C33which are single-reactor homogeneously branched and single-reactorheterogeneously branched resins, respectively. Comparative Example C32is an experimental substantially linear ethylene polymer resin producedaccording to the disclosure by Lai et al. in U.S. Pat. No. 5,272,236 andU.S. Pat. No. 5,272,272. Comparative Example C33 is a molding graderesin supplied by The Dow Chemical Company under the designation ofDowlex™ 2500.

                                      TABLE 6                                     __________________________________________________________________________    Example         23    24    25    26    27    28                              __________________________________________________________________________    First Ethylene                                                                       Polymer Type                                                                           Substantially                                                                       Substantially                                                                       Substantially                                                                       Substantially                                                                       Substantially                                                                       Substantially                   Polymer         Linear                                                                              Linear                                                                              Linear                                                                              Linear                                                                              Linear                                                                              Linear                                 Density (g/cc)                                                                         0.870 0.886 0.870 0.886 0.870 0.865                                  I.sub.2 (g/10 min)                                                                     30.0  30    30    30    3.0   8.0                                    n-Hexane 100   100   100   100   100   100                                    Extractives                                                                   Percent of                                                                             38    50    34    45    37    38                                     Mixture (wt %)                                                         Second Polymer Type                                                                           Substantially                                                                       Substantially                                                                       Hetero-                                                                             Hetero-                                                                             Hetero-                                                                             Hetero                          Ethylene        Linear                                                                              Linear                                                                              geneously                                                                           geneously                                                                           geneously                                                                           geneously                       Polymer                     Branched                                                                            Branched                                                                            Branched                                                                            Branched                                                    Linear                                                                              Linear                                                                              Linear                                                                              Linear                                 Density (g/cc)                                                                         0.940 0.940 0.935 0.935 0.941 0.946                                  I.sub.2 (g/10 min)                                                                     27    27    40    40    58    40                                     n-Hexane <2    <2    <2    <2    <2    <2                                     Extractives (%)                                                               Percent of                                                                             62    50    66    55    63    62                                     Mixture (wt %)                                                         Polymer                                                                              Density (g/cc)                                                                         0.9133                                                                              0.9132                                                                              0.9128                                                                              0.9136                                                                              0.9135                                                                              0.9137                          Mixture                                                                              First/Second                                                                           0.070 0.054 0.065 0.049 0.071 0.073                                  Polymer Density                                                               Differential                                                                  (g/cc)                                                                        I.sub.2 (g/10 min)                                                                     27.12 24.68 38.85 34.00 19.48 21.82                                  n-Hexane 9.32  6.64  10.27 6.27  4.53  16.4                                   Extractives (%)                                                        __________________________________________________________________________    Example          C29    C30    C31    C32    C33                              __________________________________________________________________________    First Ethylene                                                                       Polymer Type                                                                            Substantially                                                                        Hetero-                                                                              Substantially                                                                        Substantially                                                                        None                             Polymer          Linear geneously                                                                            Linear Linear                                                          Branched                                                                      Linear                                                       Density (g/cc)                                                                          0.940  0.935  0.886  0.913  NA                                      I.sub.2 (g/10 min)                                                                      27     40     30     30     NA                                      n-Hexane  <2     <2     100    <2     NA                                      Extractives                                                                   Percent of Mixture                                                                      26     30     32     100    NA                                      (wt %)                                                                 Second Polymer Type                                                                            Substantially                                                                        Substantially                                                                        Hetero-                                                                              None   Hetero-                          Ethylene         Linear Linear geneously     geneously                        Polymer                        Branched      Branched                                                        Linear        Linear                                  Density (g/cc)                                                                          0.903  0.9027 0.925  NA     0.9269                                  I.sub.2 (g/10 min)                                                                      30     30     58     NA     60.08                                   n-Hexane  <2     <2     <2     NA     <2                                      Extractives (%)                                                               Percent of Mixture                                                                      74     70     68     NA     100                                     (wt %)                                                                 Polymer                                                                              Density (g/cc)                                                                          0.9137 0.9121 0.9144 0.913  0.927                            Mixture                                                                              Component Density                                                                       0.037  0.032  0.039  NA     NA                                      Differential (g/cc)                                                           I.sub.2 (g/10 min)                                                                      26.24  31.00  45.28  30.00  60.08                                   n-Hexane  2.09   2.42   5.18   <2     <2                                      Extractives (%)                                                        __________________________________________________________________________     NA denotes the measurement is not applicable.                            

                                      TABLE 7                                     __________________________________________________________________________         Zone 1 Temp.                                                                         Zone 2 Temp.                                                                         Die Temp.        Extruder                                       (Actual/Set)                                                                         (Actual/Set)                                                                         (Actual/Set)                                                                        Melt Temp. Pressure                                       (°F.)                                                                         (°F.)                                                                         (°F.)                                                                        (°F.)                                                                        Extruder                                                                           (psi)                                     Example                                                                            (°C.)                                                                         (°C.)                                                                         (°C.)                                                                        (°C.)                                                                        RPM  MPa)                                      __________________________________________________________________________    23   299/300                                                                              309/300                                                                              296/300                                                                             290   190  440                                            (148/149)                                                                            (154/149)                                                                            (147/149)                                                                           143        3.0                                       24   300/300                                                                              301/300                                                                              301/300                                                                             280   190  460                                            (149/149)                                                                            (149/149)                                                                            (149/149)                                                                           138        3.2                                       25   300/300                                                                              300/300                                                                              300/300                                                                             290   190  395                                            (149/149)                                                                            (149/149)                                                                            (149/149)                                                                           143        2.7                                       26   301/300                                                                              301/300                                                                              301/300                                                                             280   190  415                                            (149/149)                                                                            (149/149)                                                                            (149/149)                                                                           138        2.9                                       C29  300/300                                                                              301/300                                                                              300/300                                                                             290   190  450                                            (149/149)                                                                            (149/149)                                                                            (149/149)                                                                           143        3.1                                       C30  301/300                                                                              300/300                                                                              300/300                                                                             279   190  440                                            (149/149)                                                                            (149/149)                                                                            (149/149)                                                                           137        3.0                                       C31  300/300                                                                              301/300                                                                              300/300                                                                             286   190  370                                            (149/149)                                                                            (149/149)                                                                            (149/149)                                                                           141        2.6                                       C33  300/300                                                                              301/300                                                                              301/300                                                                             276   190  300                                            (149/149)                                                                            (149/149)                                                                            (149/149)                                                                           136        2.1                                       __________________________________________________________________________

Examples 23-28 and Comparative Examples C29-C31 and C33 are allinjection molded at 200° C. using a 150-ton DeMag injection moldingmachine equipped with reciprocating screw and a six-cavity ASTM plaquemold to produce 6×1/2×1/8 inch (15.2×1.3×0.3 cm) flex bars. Although themelt index of the Example and Comparative Example polymer mixtures islower than the Dowlex™ 2500 resin (Comparative Example C33), all polymermixtures show good molding characteristics such as good flowability andmold filling capability as well as short cycle times. Table 8 sets forththe physical properties of the injection molded parts. Flexural modulusdetermination are performed in accordance with ASTM D790 test methods.

                  TABLE 8                                                         ______________________________________                                                                         Flexural Modulus                                     Melt Index         Density                                                                             (psi)                                        Example (g/10 min)                                                                              I.sub.10 /I.sub.2                                                                      (g/cc)                                                                              (MPa)                                        ______________________________________                                        23      27.12     6.29     0.9133                                                                              22,921                                                                        (158)                                        24      24.68     6.46     0.9132                                                                              20,430                                                                        (141)                                        25      38.85     7.07     0.9128                                                                              19,354                                                                        (133)                                        26      34.00     7.02     0.9136                                                                              20,821                                                                        (144)                                        27      19.48     7.69     0.9135                                                                              23,711                                                                        (163)                                        28      21.82     6.75     0.9137                                                                              24,486                                                                        (169)                                        C29 .sup.                                                                             26.24     6.45     0.9137                                                                              17,210                                                                        (119)                                        C30 .sup.                                                                             31.00     6.49     0.9121                                                                              17,249                                                                        (119)                                        C31 .sup.                                                                             45.28     6.94     0.9144                                                                              19,770                                                                        (136)                                        C32 .sup.                                                                             30.00     ND       0.9130                                                                              17,259                                                                        (119)                                        C33 .sup.                                                                             60.08     6.85     0.9269                                                                              36,101                                                                        (249)                                        ______________________________________                                         ND denotes the measurement was not determined.                           

As expected, due to the lower final density of the mixtures (0.913 g/cc)compared to the density of Comparative Example C33 (0.927 g/cc), theflexural modulus of the injection molded flex bars fabricated from thevarious polymer mixtures is significantly lower (32-52%) than the higherdensity LLDPE resin (Comparative Example C33).

Heat Resistance Evaluation

The injection molded parts are also tested for heat resistance tolow-frequency microwave radiation. For microwave resistance testing,Examples 23-28 and Comparative Examples C29-C33 are injection molded at200° C. into 3 inch (7.6 cm) diameter, 125 mil (0.3 cm) thick circulardisks using the DeMag molder described above and allowed to cool to anambient temperature. The disks are tested individually by placing eachdisk over a 2 inch (5.1 cm) diameter, 12 ounce (354 cc)microwave-resistant polypropylene container and filled with about 6ounces (177 cc) of commercial spaghetti sauce, i.e., Ragu® chunky gardenstyle spaghetti sauce. Each disk and container is then placed into aGeneral Electric Spacesaver® microwave for 5 minutes at the highesttemperature setting. The GE Spacesaver microwave is a typicallow-frequency consumer microwave unit. After 5 minutes in the microwave,the disk is removed, allowed to cool to an ambient temperature and thenrinsed with cool running tap water. During the rinse, the disk iscarefully held with its length parallel to the stream of tap water. Theamount of distortion for each disk is measured as warpage in centimetersby laying the disk on a flat horizontal surface and determining thedistance from the flat surface to the apex (highest point) of thewarpage. Table 9 shows the microwave heat resistance or warp resistanceresults.

To further define the heat resistance of these novel mixtures, heat sagperformance testing is also performed. Injection molded flex bars areprepared using the DeMag molder described above. The edge configurationof individual bars are recorded (printed) by firmly placing a bar edgeon a rubber stamp ink pad and stamping the configuration on a sheet ofplain paper. After the edge configurations are recorded, five bars arethen affixed to a metal rack having five spring clamps alignedvertically and spaced 3 cm apart. The bars are loaded into individualspring clamps (one bar per clamp) such that a 1/4 inch (0.64 cm) of thebar length is within the jaws of the clamp and the remaining 5-3/4 inch(14.6 cm) length is allowed to remain suspended free of any obstructionsor support. The rack containing the suspended flex bars is then placedinto a Blue M forced-air convection oven set at 100° C. for 10 minutes.After the 10 minute period, the rack is removed from oven and allowed tocool to an ambient temperature. Each bar edge is then inked again withthe inking pad and stamped on the paper adjacent to its previousconfiguration print. This second print is done in such a manner that theend of the bar that was clamped is aligned to the left of the previousedge print. Then, from the paper displaying the two prints, the maximumdistance between inner surfaces of the edge prints is measured inmillimeters and recorded. FIG. 5 graphically illustrates the properalignment of the bar prints for heat sag performance determinations. Themeasurement is repeated for each of the five bars, averaged and reportedas heat sag performance for the Example. The heat sag performance of thevarious materials is also summarized in Table 9. Examples 23-28 all showgood heat sag resistance in that lower heat sag values are taken ascharacteristic of improved heat resistance performance. Surprisingly,although Examples 23-28 have a relatively low flexural modulus as setforth in Table 8, Table 9 indicates these novel mixtures have excellentheat resistance.

                  TABLE 9                                                         ______________________________________                                                   Microwave Warp Distortion                                                                     Heat Sag                                           Example    (cm)            (cm)                                               ______________________________________                                        23         0.16 ± 0.03  1.43 ± 0.14                                     24         0.54 ± 0.05  2.61 ± 0.27                                     25         0.73 ± 0.13  2.06 ± 0.14                                     26         0.65 ± 0.13  3.14 ± 0.20                                     27         ND              1.62 ± 0.29                                     28         ND              1.29 ± 0.01                                     C29 .sup.  0.84 ± 0.05  4.59 ± 0.31                                     C30 .sup.  0.85 ± 0.04  5.40 ± 0.22                                     C31 .sup.  0.70 ± 0.09  3.22 ± 0.25                                     C32 .sup.  ND              3.84 ± 0.19                                     C33 .sup.  0.83 ± 0.12  1.13 ± 0.19                                     ______________________________________                                         ND denotes measurement was not determined.                               

Percent Residual Crystallinity Testing

The residual crystallinity of the several Examples and ComparativeExamples at elevated temperatures (100° and 110° C.) is measured bydifferential scanning calorimetry (DSC). The residual portion of thepolymer mixtures and single-reactor resins above 100° C. actuallyquantified is illustrated graphically in FIG. 6. The percent residualcrystallinity is taken from first heat determinations and calculatedaccording to the following formula:

    % residual crystallinity=(heat of fusion+292 J/cc)×% area above 100° or 110° C.

The DSC results are shown in Tables 10 and 11 and are also graphicallyillustrated in FIG. 1 for various polymer mixtures and single-reactorpolymers. From regression analysis utilizing the Cricket Graph softwaredescribed above, inventive mixtures were determined to have a percentresidual crystallinity, PRC, as defined by the equation:

    PRC≧6.4363×10.sup.4 (ρ)-3.4701×10.sup.4 (ρ).sup.2 -2.9808×10.sup.4,

where ρ is the density of the polymer mixture in grams/cubiccentimeters.

It should be noted that Example 9 in Table 10 is the same polymermixture represented above as Comparative Example C9 in Table 6. Sincethe percent residual crystallinity of Example 9 is defined by theequation immediately above and the mixture is considered useful forpreparing the molded articles of the invention, Example 9 is considereda part of the present invention. As discussed above in reference tosealant layers, the mixture is simply not preferred with respect to thefilms and coatings of the invention.

                  TABLE 10                                                        ______________________________________                                                   % Residual   % Residual                                                       Crystallinity above                                                                        Crystallinity above                                   Example    100° C.                                                                             110° C.                                        ______________________________________                                         5          1.8          0.3                                                   6          9.2          5.9                                                   7         37.8         31.7                                                   9         37.2         32.5                                                  23         33.3         29.8                                                  24         28.2         24.7                                                  25         28.9         22.9                                                  26         27.2         17.4                                                  27         30.2         24.8                                                  28         32.9         29.3                                                  C29 .sup.  20.4         16.5                                                  C30 .sup.  14.5         10.0                                                  C31 .sup.  21.6         14.6                                                  C33 .sup.  32.7         22.1                                                  ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                        Heterogeneous Linear Ethylene Polymer                                         Compara-                 Percent Residual                                                                        Percent Residual                           tive   Density Melt Index                                                                              Crystallinity                                                                           Crystallinity                              Example                                                                              (g/cc)  (g/10 min.)                                                                             at 100° C.                                                                       at 110° C.                          ______________________________________                                        C12    0.912   1.0       19.3      7.4                                        C14    0.935   1.1       42.3      33.7                                       C15    0.920   1.0       27.5      18.3                                       C16    0.905   0.8       15.2      10.4                                       C33    0.927   60.1      32.7      22.1                                       ______________________________________                                        Substantially Linear Ethylene Polymers                                        Compara-       Melt Index                                                                              Percent Residual                                                                        Percent Residual                           tive   Density (g/10     Crystallinity                                                                           Crystallinity                              Example                                                                              (g/cc)  minutes)  at 100° C.                                                                       at 110° C.                          ______________________________________                                        C13    0.920   1.0       29.1      15.0                                       C32    0.913   29.3      15.8      0.3                                        C34    0.903   30.0      1.9       0                                          C35    0.940   27.0      50.4      44.5                                       C36    0.902   3.6       4.1       0                                          C37    0.934   2.6       46.9      41.0                                       C38    0.937   2.2       49.1      43.6                                       ______________________________________                                    

Further, FIG. 1 also shows that for inventive polymer mixtures having adensity in the range of 0.900 to 0.930 g/cc, particularly in the rangeof 0.903 to 0.928 g/cc show a significantly higher percent residualcrystallinity at 100° C. than single-reactor, non-mixed polymers havingessentially the same density. As compared to a linear ethylene polymershaving essentially the same density in the range of 0.903-0.928 g/cc,Examples 7, 23, 25-28 have at least 17.5% higher, Examples 23, 25-28have at least 35% higher, and Examples 23 and 28 have at least 50%higher percent residual crystallinities. As compared to substantiallylinear ethylene polymers which are substantially amorphous at lowerdensities, Examples 7, 23, 25-28 all show dramatically higher percentresidual crystallinities.

While a higher crystallinity may explain improved heat resistance and/orhigher Vicat softening points of the Examples, it is completelyunexpected that materials with higher crystallinities also show lowerflexural moduli or lower heat seal and hot tack initiation temperatures.

We claim:
 1. A polymer mixture suitable for fabricating packaging filmsand coatings comprising(A) from 15 to 60 weight percent, based on thetotal weight of the mixture, of at least one first ethylene polymerwhich is a substantially linear ethylene-alpha olefin polymer having adensity in the range of 0.850 to 0.920 g/cc, wherein the substantiallylinear ethylene polymer is further characterized as havingi. a melt flowratio, I₁₀ /I₂ ≧5.63, ii. a molecular weight distribution, M_(w) /M_(n),as determined by gel permeation chromatography and defined by theequation: (M_(w) /M_(n))≦(I₁₀ /I₂)-4.63, iii. a gas extrusion rheologysuch that the critical shear rate at onset of surface melt fracture forthe substantially linear ethylene polymer is at least 50 percent greaterthan the critical shear rate at the onset of surface melt fracture for alinear ethylene polymer, wherein the substantially linear ethylenepolymer and the linear ethylene polymer comprise the same comonomer orcomonomers, the linear ethylene polymer has an I₂, M_(w) /M_(n) anddensity within ten percent of the substantially linear ethylene polymerand wherein the respective critical shear rates of the substantiallylinear ethylene polymer and the linear ethylene polymer are measured atthe same melt temperature using a gas extrusion rheometer, and iv. asingle differential scanning calorimetry, DSC, melting peak between -30°and 150° C.; and (B) from 40 to 85 weight percent, based on the totalweight of the mixture, of at least one second ethylene polymer which isa homogeneously branched, heterogeneously branched linear, or non-shortchain branched linear ethylene polymer having a density between 0.890and 0.942 g/cc; wherein the polymer mixture is characterized as having adensity of from 0.890 to 0.930 g/cc, and a differential between thedensities of the first ethylene polymer and the second ethylene polymerof at least 0.015 g/cc with the proviso that where the density of thefirst ethylene polymer is less than 0.887 g/cc, the density of thesecond ethylene polymer is greater than 0.920 g/cc, a Vicat softeningpoint of at least 75° C., a compositional hexane extractive of less than10 percent based on the total weight of the mixture; andwherein (a) a0.038 mm thick coextruded sealant layer fabricated from the polymermixture has a heat seal initiation temperature equal to or less than100° C. and an ultimate hot tack strength of at least 2.56 N/cm, and (b)the Vicat softening point of the polymer mixture is more than 6° C.higher than the heat seal initiation temperature of the coextrudedsealant layer.
 2. The polymer mixture of claim 1, wherein thesubstantially linear ethylene polymer has at least 0.1 long chainbranch/1000 carbons.
 3. The polymer mixture of claim 1, wherein thesubstantially linear ethylene polymer has at least 0.3 long chainbranch/1000 carbons.
 4. The polymer mixture of any of claims 1, whereinthe second ethylene polymer, Component (B), is a heterogeneouslybranched linear ethylene polymer or a substantially linear ethylenepolymer.
 5. The polymer mixture of any of claims 1, wherein at least oneof the first ethylene polymer, Component (A), or the second ethylenepolymer, Component (B), is an interpolymer of ethylene and at least onealpha-olefin selected from the group consisting of 1-propylene,1-butene, 1-isobutylene, 1-hexene, 4-methyl-1-pentene, 1-pentene,1-heptene and 1-octene.
 6. The polymer mixture of any of claims 1,wherein at least one of the first ethylene polymer, Component (A), orthe second ethylene polymer, Component (B), is a copolymer of ethyleneand 1-octene.
 7. The polymer mixture of any of claims 1, wherein themixture is prepared by mixing the first ethylene polymer and the secondethylene polymer together by at least one of the methods selected fromthe group consisting of melt mixing extrusion, dry blending, sequentialoperation of at least two polymerization reactors and parallel operationof at least two polymerization reactors.
 8. The polymer mixture of anyof claims 1, wherein at least one of the first ethylene polymer ofComponent (A) and the second ethylene polymer of Component (B) ischaracterized by a melt index of 0.1 to 75 g/10 min.
 9. The polymermixture of claim 1, wherein the compositional hexane extractive level isof at least 40 percent lower than the expected extractive amount for themixture.
 10. The polymer mixture of claim 1, wherein the compositionalhexane extractive level is of at least 50 percent lower than theexpected extractive amount for the mixture.
 11. The polymer mixture ofany of claims 1, wherein the mixture has a compositional hexaneextractive level of less than 15 weight percent based on the totalweight of the mixture.
 12. The polymer mixture of any of claims 1,wherein the mixture has a compositional hexane extractive level of lessthan 10 weight percent based on the total weight of the mixture.
 13. Thepolymer mixture of any of claims 1, wherein the mixture has acompositional hexane extractive level of less than 6 weight percentbased on the total weight of the mixture.
 14. The polymer mixture ofclaim 1, wherein the Vicat softening point of the polymer mixture is atleast 8° C. higher than the heat seal initiation temperature of the filmsealant layer.
 15. The polymer mixture of claim 1, wherein the Vicatsoftening point of the polymer mixture is at least 10° C. higher thanthe heat seal initiation temperature of the film sealant layer.
 16. Thepolymer mixture of claim 1, wherein the heat seal initiation temperatureof the film sealant layer is less than 90° C.
 17. The polymer mixture ofclaim 1, wherein the heat seal initiation temperature of the filmsealant layer is less than 85° C.
 18. The polymer mixture of any ofclaims 1 in the form of a film, film layer, coating or molded article.19. The polymer mixture of claim 18 in the form of a sealant layer orshrink layer in a packaging structure.
 20. The polymer mixture of claim19, wherein the packaging structure is a multilayer film structure. 21.The polymer mixture of claim 18 in the form of a layer in a multilayerfilm structure.
 22. The polymer mixture of claim 21, wherein themultilayer film structure is at least partly fabricated by a coextrusiontechnique.
 23. The polymer mixture of claim 21, wherein the multilayerfilm structure is a cook-in package, hot-fill package, flowable materialpouch, shrink film or barrier shrink film.
 24. The polymer mixture ofclaim 18, wherein the molded article is in the form of a storagecontainer.
 25. The polymer mixture of claim 24, wherein the moldedarticle is in the form of a storage container lid.
 26. The polymermixture of claim 24, wherein the molded article is fabricated by atleast one of the techniques from the group consisting of injectionmolding, blow molding, compression molding, rotomolding and injectionblow molding.
 27. The polymer mixture of claim 21, wherein the moldedarticle is at least partly fabricated by injection molding.